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Annals 

of the 

Missouri Botanical Garden 

Vol. 2 SEPTEMBER, 1915 No. 3 



RHIZOCTONIA CROCORUM (PERS.) DC. AND R. 

SOLANI KUHN (CORTICIUM VAGUM B. & C.), 

"WITH NOTES ON OTHER SPECIES 

B. M. DUGGAK 

Physiologist to the Missouri Botanical Garden, in Charge of Graduate Laboratory 

Professor of Plant Physiology in the Henry Shaw School of Botany of 

Washington University 

The form genus Rhizoctonia was established in 1815 to 
include two parasitic species, both characterized in part by 
the production of a mat of violet mycelium investing the 
affected roots or other submerged members. The serious 
root diseases due to these organisms (later included in one 
species) have received consideration by many mycologists 
since that time. The demonstration is comparatively recent, 
however, that several important types of root and certain 
stem and other diseases of a variety of hosts are induced by 
two or more related species of this genus. 

The literature of Rhizoctonia diseases has grown enor- 
mously in the past fifteen years, yet some unnecessary con- 
fusion and difference of opinion exist regarding the two main 
species or groups of species and their distribution and rela- 
tion to disease in plants. This is in part due to the lack of 
comparative study and to the neglect or inadequacy of her- 
barium material. It seems well, therefore, to present a con- 
spectus of the investigations relating to this subject, and to 
include such comparative data as are available. 

In cooperation with Mr. F. C. Stewart of the New York 
(Geneva) Agricultural Experiment Station, I undertook, in 
1898, a general study of the relation of Rhizoctonia to plant 
diseases in America. This joint investigation followed two 

Ann. Mo. Bot. Gahd., Vol. 2, 1915 (403) 



[VOL. 2 

404 ANNALS OP THE MISSOURI BOTANICAL GAEDEN 

independent studies, one of a serious root disease of the sugar 
beet, the other of a destructive stem rot of the carnation. A 
preliminary report upon the investigations relating to B. 80- 
lani Kiihn was published ('01), and it was arranged that in 
the further work one of us would undertake the morpho- 
logical, cultural, and taxonomic aspects of the study, and 
that the other would assume responsibility for all cross in- 
oculation and field work. Unfortunately for this purpose a 
change of position on the part of one of us and the demands of 
other work necessitated the abandonment of the plan as pro- 
posed. It is to be regretted particularly that the systematic 
inoculation experiments which had been carried forward for 
two seasons could not be continued and published. It is under- 
stood, however, that an extensive study in the relations of the 
culturable forms on different hosts has been carried forward 
both by cultural and inoculation experiments at the University 
of Illinois by Dr. George L. Peltier, who has already pre- 
sented a preliminary report ( '15), on the subject. It is mainly 
a general account of the diseases with notes on comparative 
morphology that I am able to include, but it is hoped that 
this may serve to clear up the more obvious difficulties and to 
.suggest some problems requiring special investigation. 

The writer wishes to acknowledge the assistance, mentioned 
in the text, of many mycologists who have furnished material 
during the progress of these studies, and especially the 
cooperation of Mr. F. 0. Stewart, who contributed many of 
the American hosts during the earlier studies. To Prof. 
E. A. Burt I am also indebted for suggestions. 

The Violet Eoot Felt Fungus, Rhizoctonia 
Crocorum (Pees.) DO. 

EARLY PATHOLOGICAL STUDIES 

The first mention of a plant disease which may be referred 
with certainty to Rhizoctonia as the causal agent is an impor- 
tant paper by Du Hamel (1728) read before the Paris 
Academy. In this paper he gives a careful description of a 
fungous disease of Crocus sativus (saffron) occurring in 
France. His description of general pathological features 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 405 

leaves little to be desired, and one cannot mistake the fact 
that he was discussing the disease, later known to be due to 
Rhizoctonia Crocorum. He does not describe the more minute 
morphological features, but discusses the macroscopic appear- 
ance of the mycelium and sclerotial stages with such com- 
pleteness that no doubt remains concerning the identity of the 
fungus. The illustration included would likewise confirm 
the description. He regarded the sclerotium, "tubercule," as 
the fruit body of a fungus allied to the truffles, and to this 
special form of body, assumed to bear the organs of repro- 
duction, he gave the name "tuberoides." He likewise deter- 
mined that a similar fungus is the cause of a disease found 
upon the roots of Sambucus Ebulus, Coronilla varia, Ononis 
spinosa, Muscari sp., and perhaps other plants. 

It was more than fifty years later that Fougeroux de Bon- 
daroy (1785), discussing primarily a disease of the saffron 
known as "tacon" gives further notes on the "mort du 
safran," recording the occurrence of this disease on asparagus 
when following (in the same soil) diseased -crocus. 

After a further considerable lapse of time De Candolle 
(1815) made a careful study of the pathology of a similar 
alfalfa (Medicago sativa) disease in the vicinity of Mont- 
pellier, but known throughout France. This led to the estab- 
lishment of the genus Rhizoctonia as noted later. It is neces- 
sary to the pathological account to note here, however, that 
he recognized two species, R. Crocorum DC, primarily in- 
habiting the crocus, and R. Medicaginis DC, on the alfalfa 
and other hosts. He did not follow the development of the 
fungus on the saffron, where host characteristics render some- 
what obscure the appearance of the fungus ; and so for a long 
time the continuous violet felt of mycelium was associated 
primarily with R. Medicaginis. 

Among other diseases of the carrot and beets in Germany, 
Kiihn ( '58) found typical rots of these root crops, accom- 
panied in both cases by a red-violet mycelium with other 
characteristics indicating the alfalfa organism. He identified 
the fungus as R. Medicaginis and thus established the greater 
importance of Bhizoctonia diseases, and greatly extended the 



[VOL. 2 

406 ANNALS OP THE MISSOURI BOTANICAL GARDEN 

range of the fungus. He found a somewhat similar disease 
of the potato, but clearly distinguished the fungus as another 
epecies, as further indicated in another part of this paper. 
Chief among those who extended our knowledge of the 
pathology and distribution of the violet root felt fungus was 
Eostrup ('86), who observed the fungus in Denmark and 
described its effects on various hosts. 

EARLY TAXONOMIC AND MORPHOLOGICAL ACCOUNTS 

The fungi belonging to the genus Bhisoctonia received 
attention taxonomically from the earliest mycologists. Brief 
references should be made to the works of some of those who 
have presented synopses of the genus or who have contributed 
to the solution of the problem regarding the taxonomic posi- 
tion of these fungi. Bulliard (1791) evidently based his 
description of species upon the observations and data of Du 
Hamel and de Bondaroy; emphasizing therefore the sclero- 
tium as the fruit body, and believing it homologous with the 
truffle he gave to this fungus on Crocus sativus the name 
Tuber parasiticum. He contributed nothing further to the 
morphology of the species. Persoon (1801) did not accept 
Bulliard 's disposition of the fungus, but named it Sclerotium 
Crocorum, and gave a diagnosis which, while based on the 
observations of the earlier writers, did not confuse the sclero- 
tium with a true fruit body. 

De Oandolle (1815 a ), in his first taxonomic discussion 
employed Persoon 's name for the fungus, and then, after 
giving the characteristics and parasitism of the species on 
alfalfa more careful attention, he established (1815, 1815 b ) 
the genus Bhisoctonia to include two species, B. Crocorum 
DC. on crocus and other hosts and B. Medicaginis DC. on 
alfalfa. It will be noted that he adopts Persoon 's specific 
name for the crocus fungus. De Candolle also considers a 
doubtful species, B. Mali, reported on apple. 

Nees (1816) placed the crocus fungus in Thanatophytum 
under the name T. Crocorum. Fries (1823) assigns Bhisoc- 
tonia to the Sclerotiaceae just following his extensive genus 
Sclerotium. It is important to note, since Fries' work has been 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 407 

made the starting point for mycological nomenclature, that 
he designates three species in the following order, (1) B. 
Grocorum DC, (2) B. Medicaginis DC, and (3) B. muscorum 
Fr., also giving B. Mali DC among species ignota. The 
descriptions of the two species first mentioned leave no doubt 
that he is here defining the violet root felt fungus of crocus 
and of alfalfa. Moreover, Fries recognized Sclerotium Gro- 
corum Pers. as a synonym of B. Grocorum DC So far as has 
been ascertained no specimens of these species which he ex- 
amined are still in existence. Link (1824) excluded the doubt- 
ful forms, added a species B. strobilina, and otherwise left 
the genus as constituted by De Candolle. Duby (1830) in- 
cluded among the species Bhizoctonia Allii Graves, arranging 
the genus close to Sclerotium in the Scleroteae of Lycoper- 
daceae. Fries later included in this genus B. Batatas Fr. on 
Ipomoea Batatas from America. 

The most complete mycological account of the genus Bhizoc- 
tonia is that given by L. and C Tulasne ('62). They reduce 
B. Grocorum DC and B. Medicaginis DC to a single species 
to which they apply a new name, significant of the appearance 
of the fungus, B. violacea Tul. This reduction to a single form 
was made after a most careful morphological study of the 
fungus in all stages. From the accurate descriptions and the 
excellent illustrations it is clear that they had under con- 
sideration material referable to the names above. The Tulasne 
brothers also refer to other species insufficiently known, as 
follows: B. Allii Graves, B. Batatas Fr., and B. (?) Mali DC 
They were inclined to the view that the affinities of the genus 
would be found to be with the Ascomycetes, and, in fact, they 
considered certain minute cushions of hyphae, referred to in 
detail later, as immature perithecia. Successively, therefore, 
attention was drawn by mycologists (1) to the sclerotium as a 
fruit body (Du Hamel and Bulliard), (2) to the sclerotium 
as a sterile structure (Per soon), (3) to the strand-like habit of 
the mycelium (De Candolle), and (4) to the minute cushion- 
like sclerotia as suggesting perithecia (Tulasne, L. and C). 



[vol. 2 
408 annals op the missouri botanical garden 

name, synonymy, and material examined 

Since the investigations of the brothers Tulasne many 
mycologists have studied the violet root felt fungus on its 
various hosts, especially on crocus, alfalfa, and certain root 
crops. There is general, though not complete, agreement in 
confirmation of the view that the crocus and the alfalfa forms 
are identical, and that this species, B. Crocorum, occurs on 
numerous hosts. I shall indicate later some of the morpho- 
logical details in which the two forms agree and give other 
evidence supporting the view of a single species. For the 
present it is necessary to anticipate this evidence in order to 
state that until a perfect stage is definitely established, it 
would appear that the correct designation of the violet fungus 
is Bhisoctonia Crocorum (Pers.) DC. As noted above, the 
specific name applied by Persoon was adopted by De Candolle 
when he established the genus. This name, perhaps unfor- 
tunately, has priority over B. Medicaginis DC. in that it is 
mentioned first by Fries (1823). Though necessary, it may 
seem unwise to call the fungus B. Crocorum, inasmuch as it 
is far more widely distributed on alfalfa; andp furthermore, 
because its dicotyledonous hosts are more numerous. B. vio- 
lacea would be a most appropriate descriptive name, but it 
is obvious that this also would not conform to the rules. The 
following provisional synonymy has been collated: 
Tuber parasiticum Bull. (1791), 
Sclerotium Crocorum Pers. (1801), 
Bhisoctonia Crocorum DC. (1815), 
Bhisoctonia Medicaginis DC. (1815), 
Thanatophytum Crocorum Nees. (1816), 
Tuber Croci Duby (1830), 
Bhisoctonia Bubiae Dene. (1837), 
Bhisoctonia Baud Rabenh. (1859), 
Bhisoctonia violacea Tul. (1862),- 
Bhisoctonia Asparagi Fckl. [non Fr.] (1869), 
Hypochnus violaceus Eriks. (1913). 
The identity of Bhisoctonia Crocorum DC. and B. Medi- 
caginis DC. suggested by the brothers Tulasne ('62) and 
accepted by most taxonomists, has been confirmed by a study 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 409 

of all the material I have been able to examine, and there is 
included below a list of the material identified as Rhisoctonia 
Crocorum (Pers.) DC. 

Exsiccati: Rhisoctonia Medicaginis DO, Linhart, Fung. 
Hung. Fasc. 4: 400; Rhizoctonia Dauci Rabenh., Rabenhorst, 
Herb. Myeolog. Fasc. 1 : 74. (Helminthosporium rhizoctonum 
Rabenh.) ; Rhizoctonia Solani Kiihn, De Thuemen, Myc. Univ. 
Cent. 18 : 1797. 

European collections: (1) Material from Prof. Delacroix, 
Paris, 1901, as follows : on sugar beet ; on sugar beet, obtained 
by inoculation from diseased beet; on potato; on potato, by 
inoculation from affected beet ; on crocus ; on crocus, by inocu- 
lation from affected beet; on alfalfa; on Onobrychis sativus; 
on asparagus; and on asparagus, by inoculation from dis- 
eased beet. (2) On crocus from bulb gardens, Pithiviers, 
France, 1901. (3) From Prof. Aderhold, Proskau, Germany, 
1899, on carrot and on root of young apple tree. (4) From 
Prof. Sorauer, Berlin, 1900, on potato and on asparagus. 
(5) From Herr Weigand, Helmitzheim, Bavaria, 1899, on 
alfalfa. (6) From Prof. v. Tubeuf, Munich, 1899, on sugar 
beet. (7) From Prof. Hartig, Munich, on roots of young coni- 
fer. (8) From Prof. Cugini, Modena, Italy, 1899, on alfalfa. 
(9) Material which the writer was able to obtain fresh near 
Munich, 1905, on sugar beet and alfalfa. 

In 1901 the writer was unable to find in the Kew Herbarium 
or in Paris any type material, and none was found in Mont- 
pellier in 1905. 

American collections: (1) From Mr. P. W. Graff, Man- 
hattan, Kansas, 1911, on alfalfa. (2) From Mr. F. D. Bailey, 
Laurel, Oregon, (sent by Dr. G. L. Peltier, Univ. of 111.) 1915, 
on potato. 

DISTRIBUTION 

In Europe the violet root felt fungus is in general widely 
distributed, but its occurrence now and then in epidemic form 
on some one host would appear to indicate some locality or 
race influence. On Crocus sativus the fungus has been re- 
ported from France chiefly; on asparagus, more frequently 
from France, Belgium, and Italy ; on Medicago sativa it would 



[VOL. 2 

410 ANNALS OF THE MISSOURI BOTANICAL GAEDEN 

seem to occur more commonly from southern France east- 
ward to Bavaria and Hungary and southward to the Mediter- 
ranean. No information is available with respect to its occur- 
rence in Russia. On the fleshy root crops and on the potato 
the fungus has often been reported from central France and 
Germany northward through Denmark, Norway and Sweden, 
and also on the sugar beet in Italy. In Denmark it appears 
to be found oftener on species of Trifolium than on alfalfa. 

The root felt disease is certainly not unknown to market 
gardeners and others throughout England, yet there are rela- 
tively few references to it in pathological literature. It would 
appear that Gussow has observed the fungus in England, 
for in speaking of diseased tubers from a farm in Essex 
he says, "They were covered with a dull reddish-brown web- 
bing, which was raised into numerous points, as if grains of 
sand were below it, ' ' but in view of his reference in the same 
article to the commoner potato fungus no definite statement 
should be made. Salmon's account ('08) of the disease of 
seakale, described as "a felted mass of violet -spawn or my- 
celium," evidently refers to this species. 

In the United States R. Crocorum was first reported from 
Nebraska by Webber ( '90) on lucerne. He states that it was 
rare in the Nebraska flora at that time. Heald ('06) lists 
the fungus as among disease-producing organisms prevalent 
in Nebraska during 1905. The record is as follows : "Root 
rot. Rhizoctonia violacea Tul. reported from a single locality : 
Platte County. Not common in that region. ' ' The complete 
observations made in 1906 were not reported until later, in 
which account, however, Heald ('11) fails to make note of 
Webber's earlier report of its occurrence. Freeman ('08) 
refers to the fungus as the cause of a well established disease 
of alfalfa in Kansas, and a specimen received by the writer 
in 1911 from that state indicates that it is identical with the 
European fungus. More recently it has been mentioned by 
Gandara ('10), and the inference is that it is found on alfalfa 
in Mexico. The first occurrence on potato in America is from 
a locality in Oregon (Bailey, '15). No well authenticated 
instance of the occurrence of this fungus in South America, 



1915] 

DUGGAK KHIZOCTONIA CEOCOKUM AND K. SOLANI 411 

Australia, Asia, or Africa has come to my attention, yet the 
distribution of alfalfa growing throughout the world and the 
frequent interchange of seed might suggest that the distribu- 
tion of the organism may be found to be much more general 
than is reported. It should be mentioned that Shaw ('13) 
reports the fungus from India, but he has obviously been 
misled regarding the fungus concerned, as will be shown 
later. 

Du Hamel represented the violet root fungus as prevailing 
under a variety of soil conditions, but electing dry, gravelly, 
and acid localities. It is reported by the brothers Tulasne 
that while wet weather may give the fungus an advantage, 
still it is found in the driest situations permitting crop 
growth. In central Germany Kuhn's studies led to the sug- 
gestion that on root crops and potatoes it is found more fre- 
quently in low and stagnant places. Frank and Comes con- 
cur in this view. The writer was able to observe the fungus 
in the vicinity of Munich in 1905 and in the fields examined, 
it was found under conditions which appeared to be favor- 
able for the growth of the host. The very general occurrence 
of the fungus in southern Europe, especially in southern 
France and Italy, would seem to indicate that excessive 
moisture is not always an important factor. At the same 
time the fungus is of frequent occurrence in Scandinavia. It 
is not reported as one of the more serious diseases of any 
host in England. In the more humid regions of the eastern 
United States it is unknown, while two of the localities from 
which it has been reported are regions of lower humidity and 
lesser rainfall. 

HOST PLANTS AND GBNBKAL SYMPTOMS 

There is every reason to believe that the number of host 
plants for Rhizoctonia Crocorum is much greater than has 
been reported. The fungus has been observed upon many 
economic plants ; and it has been reported in the agricultural 
press of Europe as occurring upon a variety of weeds, but 
these references are not always definite. Eriksson has made 
some observations regarding the plants attacked when culti- 



[vol. 2 



412 



ANNALS OP THE MISSOURI BOTANICAL GARDEN 



vated in soil from a carrot field known to be infected, and the 
following weed hosts are noted: Stellaria media, Myosotis 
arvensis, Galeopsis Tetrahit, Erysimum cheiranthoides, Urtica 
dioica. 

This would indicate that a careful study of any epidemic 
would confirm the view that the number of hosts is consider- 
able. The following is a list by families of the host plants 
which have been reported in the more accessible literature : 



Pinaceae 

Abies pectinata 

Picea alba 

Picea excelsor 

Pinus Laricio 

Pinus montana 
Liliaceae 

Asparagus officinalis 

Crocus sativus 

Lilium sp. 

Muscari sp. 

Narcissus sp. 

Tulipa sp. 
Urticaceae 

Ficus silvatica 

Humulus Lupulus 

Urtica dioica 
Polygonaceae 

Rumex crispus 
Chenopodiaceae 

Beta vulgaris 

Chenopodium album 
Caryophyllaceae 

Spergula arvensis 

Stellaria media 
Cruciferae 

Brassica campestris 

Brassica Rapa. 

Crambe maritima 
Rosaceae 

Crataegus oxyacantha 

Pyrus Malus 
Leguminosae 

Anthyllis vulneraria 

Coronilla varia 

Medicago lupulina 

Medicago sativa 

Melilotus alba 



Leguminosae 

Onobrychis sativa 

Ononis spinosa 

Ornithopus sativus 

Phaseolus sp. 

Trifolium hybridum 

Trifolium pratense 

Trifolium repens 

Vicia Faba 
Geraniaceae 

Geranium pusillum 
Rutaceae 

Citrus Aurantium 
Vitaceae 

Vitis sp. 
Umbelliferae 

Daucus Carota 

Erysimum cheiranthoides 

Foeniculum vulgare 

Pastinaca sativa 
Oleaceae 

Ligustrum vulgare 
Convolvulaceae 

Convolvulus arvensis 
Boraginaceae 

Myosotis arvensis 
Labiatae 

Galeopsis Tetrahit 
Solanaceae 

Solanum tuberosum 
Rubiaceae 

Rubia tinctoria 
Caprifoliaceae 

Sambucus Ebulus 
Compositae 

Taraxacum officinale 

Sonchus arvensis 

Sonchus oleraceus 



1915] 

DUGOAR RHIZOCTONIA CROCORUM AND R. SOLANI 413 

The difficulty in giving an accurate list of hosts compiled 
from the literature is, however, a serious one, since one can- 
not be certain that all the observations are carefully made. 
Again, some mycologists do not distinguish the two species 
of Rhizoctonia here discussed; thus Salmon ('08), after 
describing an interesting disease of seakale with all the 
characteristics of R. Crocorum, goes on to refer to carnation 
stem rot, damping off, and other diseases as if they were 
induced by the same fungus, doubtless, however, intended to 
have reference to another related fungus. 

Eegarding the above-ground symptoms of affected plants, 
it may be said that they are not striking, and were it not 
for the characteristic dead area in the field it would not be 
an easy matter to designate slightly affected plants. Gen- 
erally, there is in alfalfa evidence of yellowing, sometimes 
marked chlorosis, while in beets and carrots there is merely a 
paler appearanee of the foliage, followed by wilting. The 
critical period for affected alfalfa is usually about the time 
of the second cutting, and at this time considerable wilting 
may occur without preliminary indications of lack of health. 
In these main effects the disease is remarkably similar to the 
Texas root rot of cotton, alfalfa, and other plants. The un- 
mistakable symptom is the relatively sudden dying of the 
plant affected. 

The disease is generally though not necessarily fatal. Even 
a plant so susceptible as the alfalfa may recover from early 
injuries, usually with the loss of the tap root. Under cer- 
tain conditions the disease incites the development of ad- 
ventitious roots, — which may be a factor in recovery. The 
progress of the disease in the field is radial, and during the 
first year especially, circular dead areas mark its presence. 
The spread of the fungus during the season may be from a 
few feet to several rods. After the first year or two, con- 
siderable areas irregular in outline may be involved. 

MYCELIUM AND SCLEKOTIA 

It would be difficult to confuse the mycelium of the violet 
root felt fungus with any other species, for when one is 



[Vol. 



414 



ANNALS OP THE MISSOURI BOTANICAL GARDEN 



familiar with it in the different stages of development it is 
at all times an organism with striking characteristics. Such 
differences in appearance as may be found in comparable 
stages on the various hosts may be regarded as causally re- 
lated to the host substratum, or, at least they may be so re- 
garded until adequate morphological differences or contrast- 
ing physiological relations are estab- 
lished. The general appearance of 
affected roots of asparagus, carrot, 
beet, or alfalfa are well expressed in 
some of the common names applied, 
such as red root, root felt disease, 
violet fungus, etc. 

With sufficient time for abundant 
growth the fungus completely in- 
vests the root or root system with a 
mantle, weft, or mat of hyphae of 
characteristic color. In the early 
stages of growth on the root the 
mycelium is pale buff to violaceous, 
but when the root is completely in- 
Fig. 1. BHzoctonia Oro- vested, the mycelium is red-violet to 
oorum: Young hyphae. v i let-brown, and always violet- 

brown with age or when densely matted. The numerous small 
darker papillae or "minute sclerotia" in the mantle of 
mycelium are in reality cushion-like mycelial bodies described 
later. 

In the following description the writer will not attempt to 
follow all changes in the development of the various mycelial 
conditions, but will endeavor to give briefly those develop- 
mental features of greatest interest and those diagnostic 
characteristics which may be applied to most herbarium ma- 
terial. For further morphological details the accounts of L. 
and 0. Tulasne ('62) and Prillieux ('91) should be consulted. 

The external, general hyphae are more or less different in 
form and appearance with age. The younger hyphae are 
usually dilutely violaceous with a pigment which may be 
decolorized by the application of acidulated water. The pro- 




1915] 



DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 



415 



toplasm is dense towards the tips of branches and vacuolated 
farther away. The hyphae are somewhat flexuous, branched 
(sometimes closely), with the branches arising at right angles 
to the main hypha, and with a partition wall laid down at 
not over 10 n distant (fig. 1). With age the hyphae become 
rigid, somewhat less in diameter, 4-8 y., the branching is 
distant, and these branches readily break off at the first par- 
tition wall (fig. 2). At the point of union the diameter is 
uniform with the main hypha. The partition walls are distant, 




Fig. 2. Bhizootonia Grocorum: Mature root-investing hyphae. 



often 120-200 n apart. The walls now possess the violet- 
brown pigment and in the lumen little or no protoplasm is 
observable. 

The internal mycelium is likewise branched, septate, often 
associated into loose strands, passing between the cells or 
traversing them. In the early stages of the disease, so far 
as reported, these internal hyphae are nearly colorless ; Prunet 
reports that there are sometimes areas of brown mycelium in 
the attacked tissues, and this I find particularly true of 
asparagus. The internal hyphae are generally of less diam- 
eter than those constituting the external mat. 

Disregarding for the time the small cushions already men- 



[Vol. 2 
416 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

tioned, the hyphae constituting the external mantle may be 
uniformly distributed, as is the case usually when the fungus 
attacks fleshy roots or tubers, or they may also form a num- 
ber of aggregates having the appearance of loose or root- 
like strands. The strands are developed later rather than 
early in the progress of the disease. They are conspicuous 
on such hosts as alfalfa and sainfoin. These strands course 
along the whole root system; they also pass out into the 
soil, apparently beyond the minutest rootlets, and doubt- 
less attack plants in the vicinity. Upon the larger strands 
sclerotia may be formed, and thus the sclerotia are connected 
with the mantle of hyphae. 

Infection Cushions. — Small stromatic bodies distributed 
amongst the hyphae were noted by several of the early ob- 
servers. Kuhn ('58) calls special attention to them on the 
carrot and the potato. The brothers Tulasne ('62) studied 
and described them in some detail and came to the conclusion 
that these were the early stages in the development of the 
perithecial form. Search for the reproductive phase was in 
this way transferred from the sclerotium to the bodies in 
question. Sorauer ('86) among others accepted the view of 
the perithecial nature of this structure. Prillieux ( '91) seems 
to. have been the first to point out that the "corps miliaires," 
as he termed them, are in reality special mycelial cushions 
having the important function of effecting the penetration of 
the host. He regarded them as the main, if not the sole, seats 
of tissue invasion, and his studies included a comparison of 
these bodies and of the penetrating strands in alfalfa, sugar 
beet, and crocus. After mentioning these cushions as one 
type of sclerotia, Prunet designates them more specifically as 
minute "corps noiratres," .2 to 1.2 mm. in diameter with a 
brown hyphal cortex and a colorless medullar. He indicates 
that these as well as the larger sclerotia send out filaments 
which enter the soil and extend the fungus. These bodies 
have also been figured by Bailey ( '15) in the case of the occur- 
rence of the fungus on the potato in Oregon and particularly 
well by Salmon and Crompton ( '08, pi. 25). The writer is 
of the opinion that Prillieux 's notion is in general correct, 



1915] 

DUGGAR RHIZ0CT0NIA CROCORUM AND R. SOLANI 417 

and while they are not the only means of penetration they are 
most important in this connection. 

The hosts upon which the writer has had the opportunity 
to examine the infection cushions in best condition are alfalfa, 
•carrot, and asparagus. The cushions are distributed over in- 
fected roots, often 1 mm. apart in alfalfa, .5 mm. in carrot, and 
3 mm. in asparagus. The external hyphae are for the most part 
similar to those of the general mycelium, but there occur also 
branches in which the cells are short and swollen, sometimes 
resembling a short chain of spores. This form of hypha may 
have given the suggestion of a conidial stage (see Kiihn 
('58), Sorauer ('86), and others. The medullary portion of 
younger cushions is made up of finer, almost colorless hyphae, 
and it is this type which enters — strand-like — the cortical 
tissues of the root, destroying particularly the cambium and 
younger phloem regions. In the later stages of development 
it will be found that the cushions seem to extend consider- 
ably into the cortex, and more of the hyphae are colored. 

In this connection it is well to call attention briefly to some 
gross changes in the affected roots. By the time the host 
(alfalfa) reaches the critical stage, the bark slips readily 
from the root. The disintegration may continue further, 
however, through the spread of the fungus to the medullary 
rays and all other parenchyma, so that the root shreds or 
crumbles when lifted. The late stages of destruction may be 
assisted by saprophytic organisms. It is difficult to determine 
if the fungus continues its growth for a short time after the 
death of the root. At any rate, the fungus rapidly disappears 
with the further decay of the roots. 

In the case of asparagus the cushions are largely super- 
ficial and the main affected tissues are beneath the shell of 
thick-walled cells constituting the periphery of the host. In 
the carrot the invading strands are large, and the host cells 
in the vicinity rapidly collapse and darken. I have been for- 
tunate in obtaining affected asparagus roots at intervals after 
the disease had run its course. In no case could any evidences 
of spore forms be found which gave promise of genetic con- 
nection. On the contrary, the fungus gradually disappears, 



[Vol. 2 
418 ANNALS OE THE MISSOURI BOTANICAL GARDEN 

first the mantle of mycelium, and then the cushions, so that 
when the root is reduced to a mere shell there are only vestiges 
of the cushions remaining. 

Sclerotica. — The true sclerotia are flattened or rounded 
bodies varying in diameter from a few millimeters to several 
centimeters. When mature they are of a deep violet-brown 




Fig. 3. Rhizoctonia Crocorum: Cells characteristic of the tufted growth 
covering the surfaces of the large sclerotia and to a certain extent of the 
"infection cushions." 

and are thickly clothed with a persistent velvety felt, ex- 
ternally of the same color as the root-investing hyphae, but 
darkening further in. Among the surface hyphae of the 
sclerotia as well as of the "infection cushions" are found 
chains of enlarged cells (fig. 3) quite distinct from the en- 
larged cells of B. Solani. The sclerotia, as noted previously, 
are always connected with the root felt by large hyphal 
strands. In the saffron disease the sclerotia are formed both 
in contact with the shriveling bulb and also in the adjacent 
soil. On affected alfalfa roots they often occur below, and 
in the angles of, the larger branches, but often one finds no 
sclerotia in immediate contact with the host. In connection 
with diseased carrots, beets, and potatoes, they are not so 
frequent, unless perhaps they are then formed at greater 



1915] 



DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 



419 



distances from the plant. Most herbarium material, unfor- 
tunately, with the exception of crocus specimens, does not 
include sclerotia. 

In section a sclerotium consists of fairly compact tissue 
made up of cells often considerably branched and sometimes 
curiously lobed (fig. 4). 




Fig. 4. Rhixoctonia Orooorum: a, from a section of a large sclerotium; 
b, extreme forms of cells isolated from a macerated sclerotiam. 



SUGGESTIONS REGARDING THE PERFECT STAGE 

It has been noted that Du Hamel and other early observers 
stated that the affinities of the violet fungus were with the 
truffles. Persoon, Fries, and others placed the genus near 
Sclerotium. Tulasne considered the small sclerotia as prob- 
ably a stage in the development of an ascomycete (pyreno- 
mycete). This suggestion of Tulasne has apparently in- 
fluenced many mycologists, and a search in this direction for 
the perfect stage has continued practically until the 
present time. Fuckel suggested that Lanosa nivalis Fr. 
might be considered the first or conidial stage of this fungus 
and he believed that the minute sclerotia or penetration 
cushions gave rise during the latter part of the season to 
pycnidia. With the more complete disintegration of the af- 
fected tissues he reported the development of a perithecial 
stage, and this fungus he called Byssothecium circinans (Lep- 
tosphaeria circinans (Fckl.) Sacc, Trematosphaeria circinans 
(Fckl.) Wint.). It will be noted that Winter regarded this 



[Vol. 2 
420 ANNALS OP THE MISSOURI BOTANICAL GARDEN 

view of the genetic relation to Rhizoctonia as improbable; 
and Saccardo, who at first accepted the relationship, subse- 
quently changed his opinion. Prunet ('93) states that he 
made certain inoculation experiments from which he was con- 
vinced that Fuckel was correct; but we possess no indica- 
tions as to how these experiments were conducted. The 
writer in 1899, at Leipzig, germinated the spores of Lepto- 
sphaeria circinans and obtained a mycelium bearing no re- 
semblance to the Rhizoctonia hyphae. The idea that Lepto- 
spliaeria constitutes a perfect stage of the Rhizoctonia has 
had no support recently, although Comes ('91) incorporates 
it in an extreme form in his treatment of the genus. 

Rostrup ( '86) found in the spring on the old roots of af- 
fected plants a pycnidial stage which he considered to be con- 
nected with the Rhizoctonia hyphae ; and on the old roots of 
Ligustrum he found reddish filaments and scattering peri- 
thecia ; the latter he identified as a species of Trichosphaeria. 
His assumption, however, has received no encouragement. 
When Hartig ('80) discovered a Rosellinia jas the perfect 
stage of his Rhisoctonia Quercina there was a temporary re- 
vival of interest in the quest for one of the Ascomycetes as 
the perfect stage of R. Crocorum. 

Frank ('97) reported observing the violet fungus on the 
grape, and associated with it he found a species of the The- 
lephoraceae. This he regarded as the perfect stage, and to the 
fungus he applied the name Thelephora Rhizoctoniae. This 
observation has failed of confirmation. 

Eriksson ('13) has recently presented an extension of his 
earlier account ('03 a ) of diseases produced by Rhizoctonia, 
and in this he records a new "Hypochnus," H. violaceus 
(Tul.) Eriks. as the perfect stage of "Rhizoctonia violacea, 
Tul. ' ' In this he was stimulated by the observations of Rolfs 
('03) and others in America, and Pethy bridge ('11) in Ire- 
land, on the occurrence of the basidial stage (Corticium 
vagum B. & C. or Hypochnus Solani Prill. & Del.) of Rhizoc- 
tonia Solani Kuhn, resulting in a reexamination of some ma- 
terial of the violet fungus on roots and stems of certain wild 
plants. This material had been preserved in alcohol thirteen 



1915] 

DUGGAR RHIZ0CT0NIA CROCORTJM AND R. SOLANI 421 

years earlier. The result of his study is reported as follows : 

"D'apres ces renseignements, il faut — du moins pour ce qui 
concerne les formes du champignon qui envahissent les Car- 
rottes — considerer comme resolue la question tant debattue de 
savoir a quel groupe rapporter le mycelium sterile connu sous 
le nom de Rhizoctonia violacea. Dans ce qui suit, je vais in- 
diquer le nom scientifique qu'il faut donner, ainsi que les car- 
acteres diagnostiques du champignon autant que j'aie pu en 
juger sur les documents conserves que j'avais a ma disposition." 

On the basis of these observations he creates the Hypochnus 
mentioned. No adequate diagnosis is given, but the im- 
portant part of the account is as follows: 

"Ensuite le champignon forme autour des tiges de la meme 
plante ou d'autres especes de plantes immediatement au-dessus 
du sol, une enveloppe annulaire, membraneuse, d'un rose tendre, 
qui, montant souvent sur les tiges jusqua une hauteur de 5 a 
15 mm. et s'etalant parfois sur la surface du sol comme une 
feuille toute mince, produit des basidiospores. C'est le stade 
Hypochnus." 

This apparently refers to material on Stellaria media, Myo- 
sotis arvensis, Galeopsis Tetrahit, Erysimum cheiranthoides, 
Urtica dioica, and Sonchus arvensis, which hosts he would 
regard as harboring the Hypochnus stage of that form of the 
violet fungus attacking the carrot, and for this reason the 
names just given appear in the list of hosts. 

In the writer's opinion he properly considers it remarkable 
that the fructification stage should attack hosts other than 
those producing the sterile stage. In view of the character of 
the material, the incompleteness of the account, and the pos- 
sibility of confusion with Corticium vagum B. & C. it would 
appear necessary to await confirmation of the observation 
that a Corticium (Hypochnus) may represent the perfect 
stage of the fungus here discussed, although, reasoning from 
the apparent relationship of this species to R. Solani, a 
Corticium stage might well be assumed. The writer has been 
unable thus far to secure any of the material mentioned. 

In a footnote Eriksson expresses himself thus: "Quant a 
la Ehizoctone de la Luzerne, je suis porte a croire, d'apres les 



[VOL. 2 

422 ANNALS OP THE MISSOURI BOTANICAL GARDEN 

observations de cette annee (1912), quelle doit etre rapportee 
a un groupe d'Ascomycetes." This suggestion is both in- 
teresting and surprising since Eriksson adopts the Tulasnes' 
name for the Rhizoctonia on carrot and this would seem to 
concede the identity of the carrot and alfalfa forms. It is 
also in a measure inconsistent with his inoculation results, as 
reported later. 1 

CROSS INOCULATION AND CULTURAL STUDIES 

The amount of cross inoculation work yet reported is not 
considerable, and for this, doubtless, the inability to cultivate 
the organism is largely responsible. Throughout the early 
literature numerous indications are offered showing that fol- 
lowing a severe outbreak of the disease on any crop, it may 
appear on susceptible plants grown in the affected area — ob- 
servations which tend to establish the identity of the fungus 
on different hosts. Among later observations may be men- 
tioned those of Giintz ('99) who records that in a field where 
alfalfa and red clover had been seriously affected, beans, 
potatoes, and tuberous artichokes were planted^ the potatoes 
subsequently developed the disease in serious form, and the 
other plants showed indications of its presence. In England 
it is reported (Bd. of Agr., '06) that potatoes are affected by 
the violet felt fungus, especially when following alfalfa ; and 
under similar conditions the fungus appears upon clover, car- 
rots, beets, and mangolds. 

Eriksson ('13) undertook some cross inoculation work em- 
ploying, in zinc cylinders, soil from diseased carrot fields 
(eight cylinders) in contrast with soil taken from areas free 
from the disease (two cylinders). At the same time, to the 
diseased soil he added pieces of carrots affected by the 
fungus. The cylinders were permitted to stand over winter 

l Since obtaining proof of this paper I have received from Prof. Eriksson 
an advance reprint of his paper, "Fortgesetze Studien fiber Rhizoctonia violacea 
DC." Arkiv f6r Bot. 14 (Art 12) : 1-31. f. 1-13. 1915. It is impracticable to 
include here a full discussion of this paper. It is necessary to state, however, 
that he treats at length Rhizoctonia Medicaginis DC. and R. Asparagi Fckl., and 
includes inoculation experiments indicating form differences. After germinating 
the spores of Leptosphaeria circinans he comes to the conclusion that, in spite 
of his earlier work on Hypochnus violaceus, the pyrenomycete mentioned is the 
perfect stage of R. Medicaginis. Prof. Eriksson has also furnished material of 
R. Asparagi and of the Leptosphaeria. 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 423 

and the following spring were planted to several varieties 
of carrots, to beets, mangolds, red clover, and alfalfa. At 
the time of harvest, the carrots were all more or less severely 
affected, while the sugar beets and alfalfa showed very light 
attacks, and the clover none at all. Continuing the work 
in subsequent seasons he obtained evidence in one case — that 
of the sugar beet — pointing to an increased virulence of the 
fungus with adjustment to that host. On the contrary, in 
the second year the alfalfa exhibited greater resistance, thus 
rendering a decision as to the existence of physiological races 
hazardous. He also reported, that on placing diseased soil 
and diseased carrots in a box in which various weeds were 
permitted to grow, the fungus appeared on eight species of 
weeds (representing several families), apparently a consider- 
able proportion of those present. This also would seem to 
discourage the idea of marked host specialization. 

Attempts to cultivate the violet fungus on artificial media 
have been made by several investigators without success. 
While in Leipzig, 1900, I obtained particularly good material 
on alfalfa from Bavaria. Dilution cultures were attempted 
both on various kinds of agar and on gelatin, but no growth of 
the fungus was secured in any case. Further trials were 
made with material from France in 1902, and again upon re- 
ceiving comparatively fresh material from Kansas in 1911. 
Bailey ('15) reports an endeavor to cultivate the organism 
in Oregon, also without success. It is quite possible that 
special conditions are essential to its growth in artificial cul- 
ture, but we should not assume that it is incapable of growth 
in this way. It would appear that the presence of contami- 
nating organisms is not the sole cause of the difficulty, since 
isolated hyphae in the dilution cultures remain free from the 
growth of contaminating organisms, and yet themselves fail 
to develop a colony of growth. It will be recalled that At- 
kinson 1 found difficulty, but ultimate success, in growing 
Ozonium omnivorum (Lk.) Shear, the cause of the south- 
western root rot of cotton. The writer also found that this 
organism is not readily cultured, but obtained a satisfactory 

iBot. Gaz. 18:16-19. 1893. 



[Vol. 2 
424 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

growth on cotton decoction starch paste in 1902. Since in 
general pathology and physiology the cotton Ozonium and the 
violet Rhizoctonia have much in common, a further careful 
investigation of their life relations would doubtless yield 
interesting results. 

PREVENTION AND CONTROL 

Belief measures respecting the violet fungus are very 
largely limited to the practices of good culture, good drain- 
age, and sanitation. The early pathologists have generally 
recommended pulling up diseased plants and burning them. 
It is well to point out, however, that after a careful examina- 
tion of the distribution of the fungus on the smallest fibrous 
roots, it has been found to invest these to a considerable 
depth in the case of alfalfa, and therefore a very small meas- 
ure of security may be expected unless one carries out this 
recommendation in a far more thorough manner than is 
practicable in the field. The further suggestion has been 
made that where the diseased areas are few, small, and clearly 
defined, trenches may be dug to prevent the further spread of 
the disease ; but if this should prove feasible under any con- 
ditions, it would be advisable only in connection with a thor- 
ough disinfection of the isolated areas by formaldehyde or 
sulphuric acid — the former disappearing from soil in time, 
and the latter being easily neutralized by liming. The rota- 
tion of crops is undoubtedly desirable, but complete immun- 
ity from the disease cannot be expected if we may trust the 
statements of Du Hamel and other observers to the effect 
that the fungus may remain alive in the soil for periods of 
from three to twenty years. The fact that many hosts are 
affected also complicates the practice of rotation. 

The Common Rhizoctonia, R. Solani Kuhn (Corticium 

vagum B. & C.) 

EARLY STAGES 

In addition to his discussion of the violet Rhizoctonia on 
beets and carrots Kuhn ( '58) described a disease of potatoes, 
of which the causal organism was recognized as a species of 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 425 

Rhisoctonia differing notably from the violet organism, and 
to this potato fungus he gave the name R. Solani. The life 
history of the fungus and the symptoms of the disease induced 
were very imperfectly known at the time, so that the descrip- 
tion could not be complete. As a result, those who subse- 
quently discussed the genus Rhisoctonia have sometimes 
recognized R. Solani, while others have referred the organism 
to R. Crocorum (R. violacea), and still others have assumed 
that R. Solani Kiihn was also the cause of another disease of 
beets and of carrots mentioned by Kiihn without identifying 
the causal organisms. After a study of certain diseases in 
America induced by Rhisoctonia, I was keenly aware of this 
confusion, so when opportunity presented itself in the winter 
of 1899-1900 I conferred with Professor Kiihn regarding 
those diseases, and also endeavored to obtain satisfactory 
specimens of the fungi. There has been no earlier oppor- 
tunity to utilize the information obtained in connection with 
a general discussion of the genus. 

Kiihn laid special stress upon a scab ("Schorf oder Grind, " 
later termed "Pockenkrankheit") of potatoes, sometimes 
followed by deeper seated injuries and decomposition ("als 
Raude und Kratze bezeichnet"). The symptoms are clearly 
those that we now know as one type (cf. MeAlpine, '12) of 
the potato diseases ascribed to R. Solani Kiihn (Gorticium 
vagum B. & C.j. It has been noted that the fungus was not 
so well described as might be wished, and the spores men- 
tioned were evidently those of contaminating organisms, or 
else the oval cells of the tufted stage of the fungus ; but when 
we use in connection with this general description Kiihn 's 
comparison of this plant with the violet fungus (Kiihn, '58, 
p. 248) it is convincing that the fungus on the potato which 
he had under consideration was not Rhisoctonia Crocorum. 

The sclerotia were also inadequately described and figured. 
With reference to that point, however, Professor Kiihn stated 
that while a common form of the fungus on the tubers con- 
sisted of irregular superficial sclerotia, this form did not lead 
to serious consequences and therefore received less attention 
from him. Material of this superficial sclerotial stage was 



[VOL. 2 

426 ANNALS OP THE MISSOURI BOTANICAL GAEDEN 

furnished the writer by Professor Sorauer in 1900 (for a 
photograph see Duggar, '09, p. 477, fig. 219), and, subsequently, 
from other points in Germany. It is clearly the "black speck" 
form of the disease now generally recognized. Professor 
Kiihn also identified cultures of the American fungus on sugar 
beets (Duggar, '99) as very close to, if not identical with, his 
R. Solani. In 1858 Kiihn was obviously unaware of the fact 
that the violet fungus also occurs on potato in Germany; and, 
in fact, he told me in 1900 that it was subsequent to 1858 when 
he first collected specimens of the violet fungus on this host. 
"The violet fungus produces no serious epidemics of the 
potato in Germany," he declared. Professor Kiihn was un- 
able to locate type material of R. Solani, and such material 
is doubtless unavailable. Before presenting still other indi- 
cations pointing unmistakably to their identity, I shall proceed 
on the basis that it is correct to refer the sterile stages of the 
commoner American Rhizoctonia on potato and other plants 
to R. Solani Kiihn, and once studied comparatively there can 
be no confusion of this plant with R. Crocorum (Pers.) DC. 

A disease of carrots was also described by Kiihn with which 
no fungus was positively associated. The indications are in- 
sufficient to determine whether this was a fungus or a bacterial 
disease. So far as the writer is aware no disease of carrots 
in Europe due to R. Solani has since been reported, though 
in 1900 Professor Kiihn stated as his opinion that carrots as 
well as beets in Germany were affected by a fungus similar to 
R. Solani. 

The violet root felt fungus was clearly distinguished by 
Kiihn ( '58, see pp. 235-237, 243-249) in its occurrence on both 
beets and carrots. It is not possible to mistake his statements 
in which the organism on these hosts is referred to Rhizoc- 
tonia Medicaginis DC." Moreover, he nowhere suggests the 
combinations R. Baud Kiihn and R. Betae Kiihn, which later 
crept into the literature of the subject. This fact makes it 
difficult to understand the nomenclature employed by Eidam 
( '87) and Comes ( '91). In discussing a beet disease prevalent 
in Germany, Eidam refers the organism to Rhizoctonia Betae 
Kiihn. He gives a description of the disease and of the fun- 



1915] 

DTJGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 427 

gus, including its growth on culture media. It is clearly the 
beet disease now well known in America, and of which the 
causal fungus is referred to B. Solani. 

Kuhn did describe the symptoms of another disease of beets, 
and this last bears every indication of being the heart rot later 
known to be due to Phoma Betae (Phyllosticta tabifica), much 
discussed by Frank and others. Kiihn 's discussion of this 
other beet disease has been interpreted, also, in the way I 
have indicated by Prillieux and Delacroix ('91) and others 
outside of Germany. In my conference with him, Professor 
Kuhn stated that the only Bhizoctonia diseases of beets and 
carrots which he knew in the vicinity of Halle in 1858 and 
earlier were those due to the violet fungus, and of these he 
exhibited specimens having the usual characteristics. From 
the evidence at hand, therefore, the Bhizoctonia disease of 
beets described by Eidam was new on that host. It would 
seem, then, that Eidam is the authority for the combination 
B. Betae, which he attributes to Kuhn. In any case it be- 
comes a synonym of B. Solani Kuhn (Corticium vagum 
B. &C.). 

In discussing the Bhizoctonia disease of potatoes in Europe 
Sorauer ('86) describes unmistakably the "black speck" or 
sclerotial form of the fungus, and while he, like many others, 
assumed that it would be found to belong among the Ascomy- 
cetes, it is obvious that the characteristics of this stage of 
Kiihn 's fungus were well recognized. 

Among the forms of Bhizoctonia which he enumerated and 
discussed Comes ( '91) includes B. Baud Kiihn, and B. Betae 
Kiihn. In his discussion of the first-named he reviews Kuhn's 
account of the violet fungus on carrots, already mentioned; 
but in the account of B. Betae Kiihn he evidently refers both 
to Kuhn's account of the heart rot of beets and to the Bhizoc- 
tonia disease of this host described by Eidam. Pammel ('91) 
was the first American pathologist to report in this country a 
disease now known to be caused by B. Solani. He, however, 
followed Comes and Eidam in referring to the fungus causing 
the beet rot as B. Betae Kiihn. 

Atkinson ( '92, '95) studied a "sterile" fungus causing sore 



[Vol. 2 
428 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

shin or damping off in cotton, and ascertained that the same 
fungus was commonly associated with, and capable of, induc- 
ing damping off of various seedlings in the greenhouse. 

Duggar ( '99) also referred to the beet rot fungus in Amer- 
ica as Rhisoctonia Betae Kuhn, following Comes, and was 
able to determine that this beet fungus was identical morpho- 
logically (mycelium and sclerotia) with the damping off fun- 
gus found by Atkinson. The characteristics of the two organ- 
isms in culture were also identical, both forming on certain 
media a rich mycelium and finally numerous flaky or tufted 
centers of growth, some of which become irregular, often 
crust-like, sclerotia. Neither on affected seedlings nor on 
beets were sclerotia ordinarily produced (compare, however, 
Edson, '15, pi. 23). 

Subsequently, Duggar and Stewart ('01) reported that 
several types of disease, on a variety of hosts, including the 
potato, were induced by Rhisoctonia. The account given was 
intended to be merely preliminary, and for this reason a few 
words of explanation are necessary. The account referred to 
did not (perhaps unfortunately) explicitly indicate that, as 
far as the studies had progressed, there was evidence that 
the organism, or forms of the organism (except in the case 
of the form on rhubarb, referred to later) exhibited morpho- 
logically and in culture the characters of the beet rot and 
damping off fungus. The authors were likewise convinced, 
after a study of European material of Kiihn's fungus on the 
potato, of the identity of the American and European forms 
on this host. Cultural studies were being carried forward 
with Rhisoctonia Solani from many hosts, since there was 
the possibility of establishing definite forms or races, of find- 
ing the perfect stage, and of discovering other species. Again, 
specimens of the violet root felt fungus on various hosts had 
been obtained by one of us, and it was intended to include 
in a final paper a general account of the genus. 

This failure to designate the form with which we worked 
has doubtless led to some misunderstanding (see Prillieux 
'97, Eriksson '13, p. 17). However, in a more recent account 
(Duggar, '09, pp. 477-478), it will be seen that the diseases 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 429 

discussed are ascribed to R. Solani (Corticium vagum B. & C). 

DISTRIBUTION 

Rhizoctonia Solani is distributed throughout the United 
States and Canada. There is every reason to believe that it 
exists as a saprophyte in most arable soils, and under certain 
conditions may attack many species of plants. It is perhaps 
most frequently noted as a damping off disease in green- 
houses and seed beds, but this occurrence may be explained 
by the fact that here the conditions are probably more con- 
ducive to the pathogenicity of the fungus. On the potato 
it is likewise wide-spread, although, as noted later, the eco- 
nomic importance of the diseases induced varies in different 
sections of the country, probably in accordance with climatic 
and soil conditions. In all potato-producing states and re- 
gions it is a well-known disease. On the sugar beet it has been 
observed in many states. The fact that it is an important 
disease of one crop or another in every section of the country 
is alone sufficient indication of its general occurrence. Rhiz- 
octonia has been mentioned in Brazil by Potel^OO), but it is 
not clear to which species he refers. 

It is rather surprising to find that R. Solani has received 
relatively little attention in Europe. Although recognized as 
inducing a disease of the potato widely distributed in central 
Europe, and occasionally reported on the beet, yet little care- 
ful work has been bestowed upon the fungus. Eriksson ( '13), 
seems to be unfamiliar with the fungus in Sweden. On this 
account we can gain no incidental information regarding R. 
Solani as a result of his extensive studies of the related spe- 
cies in that country. The following will express his attitude 
regarding R. Solani: 

"II parait tres douteux, du moins si l'on en juge d'apres les 
descriptions et les figures donnees, que les nouvelles formes de 
la Rhizoctone sterile signalees dans ces derniers temps par B. M. 
Duggar et F. 0. Stewart sur une quantite de plantes differentes 
en Amerique (* * *) soient vraiment identiques aux formes 
du Rhizoctonia violacea qui ravage l'Europe." 

We have very little data regarding its occurrence in other 
sections of continental Europe, although from conference 



[Vol. 2 
430 ANNALS OE THE MISSOURI BOTANICAL GARDEN 

with Prof. Delacroix in Paris (Nov. 28, 1901) and from an 
examination of material furnished by him I learned that it is 
not uncommon throughout France on the potato. It will he 
recalled that the perfect stage was described by Prillieux and 
Delacroix ('91). Judging from the amount of the black 
speck disease observed on the potato in the markets of various 
cities in southern Europe during 1905- '06 the writer would 
infer that it is of more frequent occurrence than is reported. 
Pethybridge ( '11) finds the fungus (including the Corticium 
stage) well distributed in Ireland, and it is reported from 
other parts of Great Britain. 

McAlpine ( '11) has reported this fungus on the potato from 
several points in Australia, and he states that it occurs upon a 
variety of economic plants. Since it has proved a serious 
disease in very few localities, it receives little attention, and 
is therefore freely disseminated by commercial intercourse. 
It is also known in New Zealand and Japan. 

The investigations of Shaw ('13) suggest that Rhizoctonia 
Solani may be an important disease-inducing organism in 
some of the more humid regions of India. Reference is made 
later (pp. 448^50) to the fact that he has obviously misap- 
plied this name, however, and also that other confusion has 
resulted. In spite of this, it seems certain that he has ob- 
served all stages of the fungus. 

TYPES OF DISEASES INDUCED, SYMPTOMS 

It is not my purpose to attempt a complete description of 
the more important diseases caused by this species, yet suf- 
ficient will be included to indicate the main types of diseases 
thus far investigated, their general distribution, and their 
striking pathological relations. By types of disease, I have 
reference to general effects or symptoms. The effect of the 
fungus upon the stems may occasion a different appearance 
from its action upon the root, and thus there arise the differ- 
ent types referred to. With respect to penetration and action up- 
on the cell the behavior of the fungus may be the same in 
all cases. Moreover, as a result of the primary injury, second- 
ary effects may occur, and sometimes such secondary phe- 



1915] 

DUGGAR RHIZ0CT0NIA CROCORUM AND R. SOLANI 431 

nomena may be so striking in appearance as to dominate the 
primary injuries or lesions. 

For convenience we may arrange the types of disease in the 
following categories : (1) damping off, (2) stem rot, (3) root 
rot, (4) leaf rot, (5) scab, and (6) such secondary effects as 
rosette, little potato, and leaf roll. Since more than one type 
of disease may occur upon a single host, and especially since 
one form of the disease may grade into another, it will be more 
practicable to discuss these under the following captions: 
(1) damping off, (2) potato diseases, (3) rot of fleshy roots, 
(4) stem and root rots of herbaceous plants, and (5) fruit 
and leaf injuries. 

DAMPING OFF 

It would appear that the first mention of a disease of seed- 
lings caused by Rhisoctonia is that of beets, recorded by 
Eidam ('87), although he gives no complete account of the 
evidence. It is preferable to date our knowledge of damping 
off diseases caused by Rhisoctonia from the work of Atkinson 
('92), who studied particularly sore shin of. cotton, but he 
also found the "sterile" fungus to cause damping off 
of seedling beets, radish, lettuce, egg plants, cabbage, and 
other plants in the forcing house. The later identification 
of the fungus concerned (Duggar, '99) and its association 
with the damping off of various plants (Duggar and Stewart, 
'01) was only the beginning of the observations which have 
now served to direct our attention to the vast importance of 
this fungous disease throughout the United States both in the 
greenhouse and in the outside seed bed. 

Among numerous instances in which damping off has been 
reported due (or in all probability due) to this fungus may be 
noted the following: (1). It has been found as a source of 
serious injury to ginseng in the seed bed (Van Hook, '04; 
Whetzel and Rosenbaum, '12). (2). Tobacco seedlings are 
so frequently injured that soil treatment has received special 
consideration in the case of this crop (Selby, '04; Cook and 
Home, '05). (3). As a damping off disease of cotton (sore 
shin) it occurs not only in America but in Africa (Balls, '05, 
'06) and possibly in India (Shaw, '13) as well. (4). Tomato 



[vol. 2 

432 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

seedlings seldom attacked by Pythium have been found to 
succumb to Rhizoctonia in Louisiana (Edgerton and More- 
land, '13). (5). Alfalfa seedlings have been reported sus- 
ceptible in one instance (Stewart, French, and Wilson, '08). 
(6). Seedlings of various species of conifers from a few days 
to nine weeks old have been reported attacked in several in- 
stances (Hartley, '12, Clinton, '13). 

The majority of the instances reported above were under 
normal seed bed or field conditions. Many other cases of the 
damping off of seedlings might be included where seeds are 
grown in crowded condition in moist greenhouses. Again, 
damping off of cuttings by Rhizoctonia is now a well-known 
phenomenon in the propagating house, and special precau- 
tions are taken with respect to drainage and moisture in order 
to reduce the injuries to a minimum. It is safe to assume — 
since the fungus seems to be found in practically all soils — 
that it is in general the worst enemy of seedling plants. In 
fact, it may be anticipated that under conditions favorable for 
the fungus the damping off of seedlings of numerous species 
may be anticipated. So far as the writer has been able to 
ascertain there has been no report of the damping off of mon- 
ocotyledonous plants under normal seed bed conditions. 

"While Rhizoctonia Solani may perhaps induce damping off 
in innumerable species regarding which observations are 
lacking, some of the host plants which have come to the writ- 
er's attention as particularly susceptible are the following: 
lettuce (Lactuca sativa), celery (Apium graveolens), beet 
{Beta vulgaris), cress (Lepidium sativum), tobacco (Nico- 
tiana Tabacum), balsam (Impatiens balsamina), snapdragon 
(Antirrhinum ma jus), cotton (Oossypium spp.), cucumber 
{Cucumis sativus), squash (Cucurbita spp.), sunflower (Eeli- 
anthus annuus), carrot (Daucus Carota), radish (Raphanus 
sativus), and phlox (Phlox Drummondii). 

Since the phycomycetous damping off fungus Pythium has 
been known to pathologists much longer, and prior to 1895 
was practically the only fungus to which this type of disease 
was ascribed, it is probable that much damage due to Rhi- 
zoctonia has been ascribed to Pythium. Moreover, unless 



1915] 

DUG«AR RHIZOCTONIA CROCORUM AND R. SOLANI 433 

examined microscopically, there are no symptomatic differ- 
ences between the effects of the two organisms. 

Seedlings affected exhibit symptoms somewhat different with 
age. The youngest seedlings of all delicate plants show what 
may be called the usual damping off characteristics. Near the 
base of the stem an hygrophorus or translucent appearance 
is quickly followed by shrinkage of the tissues and weakness 
of the stem. The plants topple over, the fungus invades all 
parts, and spreads rapidly to the neighboring individuals. 
The cells of the sap-perfused tissues are flaccid and injured, 
some showing this even before the entrance of the hyphae into 
the cells. Somewhat older plants and the more robust seed- 
lings of cotton, bean, etc., often exhibit characteristic lesions. 
Atkinson ('95) gives a description of its effect on cotton 
seedlings as follows : 

"The trouble is caused by the fungus growing first in the 
superficial tissues of the stem near the ground and disintegrat- 
ing them before it passes to the deeper tissues; in other words 
the fungus never seems to penetrate far in the living tissues, 
but 'kills as it goes,' and the tissues become brawn, depressed, 
and present the appearance of the plant having a deep and 
ugly ulcer at the surface of the ground. The fungus does not 
spread into the tissues either above or below the ulcer to any 
extent, but literally eats away at that point until it has severed 
the stem at the affected place or the plant has recovered from 
its effects." 

DISEASES OP POTATOES 

The potato is the most interesting of the host plants with 
respect to the parasitism of Rhizoctonia by reason of the 
many types of disease induced under diverse conditions. The 
conditions may be in part climatic and, in part perhaps, de- 
pendent upon the pathogenicity of the particular strain of the 
fungus or upon the stage and development of the host at the 
time of infection. It has been noted that when Kiihn first de- 
scribed the disease of potatoes in Germany he laid emphasis up- 
on a scab which was often followed or accompanied by decay. 
This form of the disease was probably less prevalent in the 
country as a whole at that time, and the more recent accounts 
indicate that the "black speck scab" or "black speck," prop- 
erly the sclerotial stage, is the feature by which the main type 



[Vol. 2 
434 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

of the disease is now generally known. At present the following- 
main types of injury are recognized for the potato : (1) black 
speck scab or sclerotial stage, (2) Rhizoctonia scab, (3) Rhizoc- 
tonia rot, (4) stem lesions and root rot, (5) rosette and leaf 
roll, and (6) little potato and aerial potato. 

Black speck is a form of the disease most widely distrib- 
uted and in itself scarcely merits consideration as a "dis- 
ease" at all, since the sclerotia are superficial on the tuber, 
and it is merely the appearance of the potato which is affected. 
The sclerotia may lead to other types of disease which are 
more serious. The black specks show up most clearly when the 
potatoes are wet and it is only at this time that they present 
the appearance of being black, for, as indicated later, the nor- 
mal color of the sclerotia is deep brown. It was this form of 
the disease which first gave evidence of the wide distribution 
of the fungus in America (Duggar and Stewart, '01), and it 
has been shown to exist in practically all potato-producing sec- 
tions of the United States and Canada. It occurs throughout 
Europe, especially on the later varieties of potatoes. It is also 
reported from India, Africa, and Australia, so that it may be 
assumed to be world-wide in its distribution on this host. It is 
safe to say that this is the only form of the disease which does 
not result directly in serious injury and loss to the crop. In the 
United States, especially from Ohio westward, other forms of 
the potato disease assume a seriousness nowhere else attained. 
If all such forms of the disease mentioned below occur in the 
Atlantic states they are of little consequence. They are, more- 
over, far less frequent in Europe, India, and Australia. 

The Rhizoctonia scab is believed to occur as a result of the 
penetration of hyphae during the early stages of sclerotial 
development, and occasionally it may be induced by a late 
growth of new hyphae from old sclerotia. The writer has had 
an opportunity of examining only casually this form of the dis- 
ease. It is one of the types doubtless seen by Kuhn. Accord- 
ing to McAlpine ('11), when this disease occurs, practically 
every part of the tuber is affected, no normal skin remaining. 
In severe cases the scab areas may be thrown into folds or 
puckers and these rub off easily in the form of "cork dust." 



1915] 

DUGOAE BHIZ0CT0NIA CEOCOEUM AND E. SOLANI 435 

It is reported that the irritating hyphae are then found at 
the bases of such scab formations. This scab has been re- 
ported fairly common in Europe and in Australia. Giissow 
('05) seems to refer to the same type in England, and Rolfs 
( '03) describes it from Colorado. Specific scabs of the potato 
have been clearly defined and related to particular organisms. 
The capacity of the tuber to respond with cork formation to 
varied injuries suggests that in certain modifications of Rhi- 
zoctonia scab this fungus may accompany other active scab 
inducing agents. 

The Rhizoctonia rot is a form of disease which appears rel- 
atively late in the season when certain conditions prevail, or 
possibly when the fungus has for one reason or another de- 
veloped unusual virulence. The disease is supposed to origi- 
nate either from stem infections, from sclerotia, or from scab 
areas. In any case penetration of the mycelium occurs to a 
considerable depth, and according to McAlpine ('11) there is 
produced in Tasmania a form of the disease known as brown 
rust, characterized in the early stages by dark spots in the 
tuber resembling certain symptoms of Phytophthora. It may 
also be associated more or less with the deeper form of the 
Rhizoctonia scab. During the latter part of the season a typi- 
cal stem rot may occur which is not characterized by the 
definite lesions described later. Instead, the affected cortex 
slips readily from the wood and about the bark a considerable 
web of the yellow-brown hyphae may be found superficially, 
below and just at the surface of the ground, and the pith may 
be fairly stuffed with the mycelium. Plants only slightly af- 
fected with this form of the disease, especially when growing 
on rich garden or muck soil, have been found to yield the 
collar or Corticium stage. 

It is not always easy to distinguish as separate forms of 
the disease, stem lesions, rosette, little potato, aerial potato, 
rolling, etc., for these types of injury are often associated. All 
of these types except stem lesions are properly secondary ef- 
fects, and there is abundant evidence that all represent 
responses of the plant to disturbed condition or nutrition, 
sometimes associated with native weakness. It would not be 



[Vol. 2 
436 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

strange, therefore, if somewhat similar effects should charac- 
terize, as they do, purely "physiological" disturbances. Stem 
lesions are generally dark, sunken areas, clearly different from 
black leg, occurring at the surface of the ground or on any of 
the underground stems, or tuber-forming stolons. These 
lesions may result in the early death of the affected plants. 
Selby ('02, '03) maintains that generally the lesions upon 
young shoots are associated with stunted growth and the pro- 
duction of rosette-like clusters of the upper leaves, as well as 
with less marked modifications of habit, including slight leaf 
rolling. Drayton ('15) finds the hyphae in the lesions. 

If the tuber-bearing stolons are the seat of injury, the food 
supply is cut off from the young tubers and there may result 
"little potato," a form of the disease which Rolfs ('04) has 
found to be an important cause of the potato failures in 
Colorado. Little potato in Australia is considered an evi- 
dence of underground injuries occurring late in the season. 
Injuries which effectually girdle the stem, especially if these 
occur during a moist season or when the cropis frequently 
irrigated, lead to the formation of aerial tubers. In the re- 
lation of Rhizoctonia to the various types of potato diseases 
much remains to be investigated, and Orton ('14) rightly 
suggests that inadequate attention has been bestowed upon 
the question of the predisposition of the tubers used as seed, 
since it is quite possible that these may yield offspring with 
tendencies toward rosetting, leaf rolling, and other morpho- 
logical modifications. 

EOT OF FLESHY ROOTS 

The root rot of beet, apparently first described by Eidam 
( '87) in Germany, and shortly afterward found by Pammel 
('91) in Iowa, was observed in New York (Duggar, '99) some 
years later. Since that time it has appeared epidemically 
in Nebraska (Lyon and Wianco, '02) and other western states. 
The fungus is most virulent during midsummer or later. In- 
fection may take place at the bases of the leaves or on the 
fleshy root. The leaf bases blacken, the leaves become paler, 
and finally wilt. Pammel ('91) has drawn attention to the 



1915] 

DUGOAR RHIZOCTONIA CROCORUM AND R. SOLANI 437 

fact that when fleshy root crops of this type are attacked by 
such fungi they die gradually, while herbaceous plants (cot- 
ton, alfalfa, etc.) wilt suddenly. This is probably closely re- 
lated to the effect of the fungus on the conducting tissues. 
In the beet root the invaded tissues are pale brown, and often 
cracks or rifts occur, though rotting may take place without 
such lesions. Sometimes there is partial recovery after the 
cracks are formed, and in this case callous tissue is developed. 
A soft crown rot of the radish induced by this fungus has 
apparently been reported only once (Duggar and Stewart, 
'01). A similar disease of the carrot was found in 1900 in 
New York and this is possibly the disease first reported by 
Kiihn ('58, pp. 241-243), although he did not identify it as 
due to a Rhizoctonia. 

STEM AND ROOT ROTS OF HERBACEOUS PLANTS 

Rhizoctonia Solani produces serious stem and root rots of 
a number of economic herbaceous plants, among which the 
following are known to be important: carnation (Dianthus 
caryophyllus) , Sweet William (Dianthus barbatus), bean 
(Phaseolus vulgaris), sweet-pea (Lathyrus odoratus), and 
violet (Viola odorata). 

The carnation stem rot is one of the most destructive dis- 
eases occurring on this host and is wide-spread in the United 
States. The general symptoms of the disease on carnation 
and Sweet William are much the same. The stem is affected 
at or just below the soil level. The fungus penetrates and 
kills the cortex which may be readily slipped from the wood. 
Through the medullary rays the hyphae also enter the pith, 
which likewise decays. In later stages of the disease the 
wood shreds, due to the complete penetration by the fungus 
of all parenchymatic tissues. 

Several important epidemics of Rhizoctonia on bean have 
been reported from different parts of the United States. In 
addition to the outbreak described by Duggar and Stewart 
('01), Hedgcock ('04), a few years later, found the bean dis- 
ease severe near St. Louis. The base of the stem and the 
larger roots bore characteristic ulcerations; pods were af- 



[Vol. 2 
438 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

fected, and through the sunken areas of these the hyphae 
penetrated the seed and produced small sclerotia on the seed- 
coats. The fungus was cultivated and typical Ehizoctonia 
hyphae and sclerotia were obtained. Fulton ('08) observed 
the disease in Louisiana on stems and pods, with the char- 
acteristic ulcerations, especially at the surface of the soil or 
just below. He proved the causal relation of the organism 
through cultures, and inoculations yielded positive results 
with the damping off of seedlings. McCready ( '10) reported 
the bean disease as new to Ontario, where it was also char- 
acterized by stem and pod ulcers. In New York Barrus ( '10) 
observed an epidemic of this host in which as many as 30 
per cent of the plants were affected. He determined the 
fungus by cultural studies and proved its pathogenicity by 
inoculation. On the sweet-pea the disease is mainly a root 
rot, yet the base of the stem may also be considerably affected 
before the plant succumbs. On the violet it is primarily a 
crown disease, but where the plants are succulent and the con- 
ditions are moist, the leaves are considerably, invaded. 

FRUIT AND LEAF INJURIES 

In discussing stem diseases the occurrence of Rhisoctonia 
on bean pods has been mentioned. Another case of fruit 
injury is described by Wolf ('14), who found a severe rot of 
egg plant fruits from which the fungus was obtained. The 
pathogenicity of the organism was determined by inocula- 
tions, and cross inoculation from tomato and potato led to 
the conviction that the organism was Rhisoctonia Solani. 

Direct attacks of leaves by Rhisoctonia Solani are infre- 
quent. From the habits of the fungus this would be expected. 
The one serious leaf disease reported is that of lettuce ( Stone 
and Smith, '00), in which the fungus spreads over the whole 
surface, causing a moist rot. Sclerotia are frequently formed 
in connection with this affection. It would be anticipated, 
perhaps, that diseases of a similar nature might be found on 
other plants with the rosette habit. Leaf stalks are fre- 
quently invaded, or may be the regions of first attack, in the 
case of the beet disease. The disease of leaf stalks of rhubarb 



1915] 



DUGGAR RHIZ0CT0NIA CROCOKUM AND R. SOLANI 



439 



reported by Duggar and Stewart ('01) is not due to typical 
R. Solani. 

MYCELIUM AND SCLEROTIA 

The morphological characteristics of the hyphae and 
sclerotia have been adequately described by several writers, 
but it may be well to summarize some of the more important 
features. Upon such hosts as the 
potato, sugar beet, carnation, and 
others there is more or less de- 
velopment of an external web, 
but never over the general root 
system such a complete invest- 
ment of roots by a mantle of 
hyphae as characterizes the violet 
fungus. The external hyphae are 
somewhat colored, usually yellow- 
ish brown, and they are generally 
of two types. One type may be 
designated as purely vegetative 
and another as constituting the 
external tufts or masses when 
these occur. All hyphae are prac- 
tically colorless when young, vac- 
uolate, more or less irregular, 
septate with the septa at intervals 
of 100-200/«. The diameter of 
vegetative hyphae is 8-12 ft. 
Branches arise, and when young 
these are inclined in the direction 
of growth and are invariably somewhat constricted at the 
point of union with the main hyphae (fig. 5). As the hyphae 
mature and become more deeply colored they are more uni- 
form and rigid, the distances between cross walls are greater, 
the constrictions where branches arise less marked, and the 
branches are approximately at right angles to the main hypha. 

On certain affected plants a short tufted or mealy growth 
occurs and this is made up of hyphae of very different char- 
acteristics. In the young condition threads are profusely 




Fig. 5. Rhizootonia Solcmi ( Oor- 
tidum vagum) : A vegetative 
hypha and a small strand from 
artificial culture on potato. 



440 



[vol. 2 



ANNALS OP THE MISSOURI BOTANICAL GARDEN 



branched and lobed, sometimes botryoid, and they are ulti : 
mately divided into short, ovate cells, arranged in short 
chains, or elbowed, and producing branches in a more or less 
dichotomous fashion (figs. 7 and 8). In culture the denser 





Fig. 6. Rhizoctonia Bolwm : 
Vegetative hyphae. 



Fig. 7. Rhizoctonia Solami: a, 
young hyphae from young sclero- 
tial tuft on lettuce; b, older cells 
from same source. 



masses give rise to sclerotia. With maturity these hyphae be- 
come light brown in color, they break up readily into short 
hyphal lengths or single cells, the individuals of which bear 
some resemblance to conidia. However, they could not easily 
be mistaken for spores, although they may function as such, 
inasmuch as most of them may germinate within a few hours 
when placed under suitable conditions. I have previously de- 
scribed ('99) this process as follows: 

"So far as observed, germination is always by the protrusion 
of a tube through a septum. When several cells are connected, 
a germ tube from one cell may pass into and through its 
neighbor, * * * *, and thus peculiar appearances may result. 
Some of the cells of the hyphal chains seem to be devoid of 
protoplasm, and from neighboring protoplasmic cells the germ 



1915] 

DXJGGAE RHIZOCTONIA CBOCOBUM AND R. SOLANI 441 

tubes seem to pass into such empty cells as readily as directly 
into the nutrient solution. When the germ tube is from 10 p 
to 20 fi in length, it is invariably narrowed towards the outlet 
from the parent cell, and a septum forms at a short distance 
from this outlet." 




Fig. 8. Rhigoctonia Solcmi: Lobulate, moniliform, and elbowed cells from 
tufted growth in artificial culture. 

The hyphae which penetrate the tissues remain colorless so 
long as they are in active growth, and while generally less 
in diameter they present much the same appearance as the 
young external hyphae. In the different strains which have 
been studied, originating from different hosts, certain minor 
modifications of the general habit of the fungus in culture 
have been observed. But these have not seemed to be suffi- 



[Vol. 2 
442 ANNALS OP THE MISSOURI BOTANICAL GARDEN 

cient to be considered of specific importance, except in the 
case of the form on the rhubarb. In general, the differences 
referred to consist in a variable amount of the mealy or 
tufted growth, or of the amount of aerial growth; differences 
in the color of the colony are also observable ; and the rapidity 
with which sclerotia are formed are all minor distinguishing 
features. The subject needs further investigation, but in gen- 
eral it is felt that these differences are such as might be due 
to permanent differences in the pathological strains, on the 
one hand, or may be regarded as temporary differences due 
to the recent environment, on the other. It may be pointed 
out that the appearance of the mycelium of the beet fungus 
from the damping off seedlings is not exactly comparable 
with that of the mycelium derived from the beet rot. When 
the organisms from both sources are grown in culture they 
are found to be identical. Strains do occur, however, evidence 
of which may persist for some time in the general appearance 
of the cultures. 

The exact conditions under which sclerotia may occur on 
the various hosts affected have not been determined. It has 
been noted that affected potato tubers are the main seats of 
sclerotia formation when the fungus attacks that host. Upon 
this plant they are typical, and the numerous illustrations 
published are sufficient evidence that the appearance is much 
the same under a variety of conditions. Special attention 
may be called to the illustrations of Duggar and Stewart 
('01), Eolfs ('02), Duggar ('09), McAlpine ('11), Pethy- 
bridge ('11), and Morse and Shapovalow ('14). On the 
majority of hosts, however, sclerotial formation is relatively 
rare. 

From the various illustrations referred to it will be seen 
that the sclerotia vary in size from those so minute as to be 
scarcely visible, to others which may be a centimeter or two 
in diameter. They are generally more or less flattened, 
irregular, deep chestnut-brown, and generally smooth on the 
surface (that is, free from a looser growth of investing 
hyphae). Smoothness of sclerotia, which has been regarded 
by Kiihn as of much diagnostic value, should not be considered 



1915] 



DUGGAR RHIZOCTONIA CR0C0RTTM AND R. SOLANI 



443 



an important character except under natural conditions. 
Sclerotia which develop on fleshy organs in moist chambers 
as well as those which develop in culture show to a certain 
degree, a semi-persistent hyphal investment ; but such invest- 
ing hyphae are readily worn away, whereas in the violet 
fungus they are truly persistent. 

Sections of the denser sclerotia exhibit a fairly homo- 
geneous structure (fig. 9), with the cells more uniform in size 
and appearance than in Rhizoetonia Crocorum. 





Fig. 9. Rhizoetonia Solani: a, from a section of sclerotium on potato; b, 
cells isolated by maceration of sclerotium. 



THE BASIDIOSPORE STAGE, SYNONOMY, AND MATERIAL EXAMINED 

Besides suggestions of a general nature no indications 
regarding the perfect stage of Rhizoetonia Solani were made 
prior to the discovery of the Corticium. Prillieux and Dela- 
croix ('91) described Hypochnus Solani from potato stems, 
and although at this time the Rhizoetonia diseases were 
known in Europe no connection with this Hypochnus stage 
was suspected. The characteristic collar of mycelium was 
found surrounding the stem just above the surface of the 
ground, but they found nothing to indicate that the fungus 
had injured particularly the plant affected. 

Rolfs ('03) found the collar fungus during his studies of 
potato diseases in Colorado. The material was determined 
by Prof. E. A. Burt as referable to the species Corticium 
vagum B. & C. On account of the parasitic habit, however, 



rvou 2 

444 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

it was considered advisable to make the fungus a variety of 
the Berkeley and Curtis species, so that it was written Gor- 
ticium vagum B. & C. var. Solani Burt. Prof. Burt also recog- 
nized that it agreed closely with, and might be identical with, 
Hypochnus Solani Prill. & Del. This conclusion the writer 
accepts, but in view of the fact that Professor Burt is pre- 
paring a monograph of the Thelephoraceae, I shall not dis- 
cuss this point ; for the same reason I need only express doubt 
regarding the validity of Shaw's suggestion that Hypochnus 
ochroleucus Noack and Corticium vagum B. & C. are identical, 
although there is a certain similarity in the various stages. 

Rolfs ('04) was able to germinate the basidiospores and 
to develop characteristic Rhizoctonia hyphae from these. 
Riehm ('11) also reported germinating the basidiospores and 
producing a characteristic Rhizoctonia mycelium together 
with the formation of sclerotia. Pethybridge ('15) gives a 
more complete account of mycelial production from spores. 

The herbarium and fresh material which has been examined 
and found to agree with the authentic descriptions of Rhizoc- 
tonia Solani Kiihn {Corticium vagum B. & C.) may be briefly 
enumerated : 

Exsiccati : Rhizoctonia Napaeae nov. sp., Westendorp and 
Wallays, Herb. Crypt. Fasc. 5: 225. (On decaying turnips 
which had been stored in a cave.) 

American material: Hyphal stages on numerous hosts, 
many of which are mentioned in this paper, also others not 
included; sclerotia, on potatoes grown throughout the eastern 
and central United States, on potato stems (New York, 1900), 
on bean pods (New York, 1910), also on carnation stems, let- 
tuce leaves, etc. Corticium stage from Prof. F. H. Rolfs, 
Colorado, 1901, on potato stems; from Dr. I. C. Jagger, 
Rochester, New York, 1914, on potato stems and on crown 
of carrot; from herbarium of Prof. E. A Burt, material on 
moist soil and decayed wood, collected by Prof. Farlow, Mag- 
nolia, Mass., 1903; from Herb. Mo. Bot. Garden, Nos. 44679, 
44681, and 44682 ; collected by Dr. Geo. L. Peltier, Urbana, Dl, 
1915. 

European material : Sclerotia on potato tubers from Prof. 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 445 

Sorauer, Berlin, 1900; from Prof. Magnus, Berlin, 1901; from 
Prof. Delacroix, Paris, 1901; and material secured on the 
markets of various cities, 1905-06. 

As far as the writer has been able to determine, the fol- 
lowing synonomy may be listed for Corticium vagum B. & C. : 

Rhisoctonia Solani Kuhn (1858). 
Rhisoctonia Betae Eidam [non Kuhn] (1887). 
Rhisoctonia Napaeae West. (1846). 
Rhisoctonia Rapae "West. (1852). 
Hypochnus Solani Prill. & Del. (1891). 

PREVENTION AND CONTROL 

Much the same situation confronts us regarding the pre- 
vention and control of Rhisoctonia Solani as in the case of 
R. Crocorum. The presence of the fungus in practically all 
soils serves to emphasize the importance of cultural methods 
including drainage and sanitation. In this case, however, 
since the fungus is of so much importance in the. seed bed and 
in the greenhouse special preventive measures may be prac- 
tised. Selby ('06) found that the treatment of the seed bed 
with formalin (1 : 160 to 1 : 200) proved satisfactory in most 
cases. In general, the best results have been obtained by 
steam sterilization, and where the facilities are at hand it is 
practicable to apply this to any type of greenhouse work, and, 
in certain cases, to seed beds outside. Liming has been recom- 
mended for the control of the disease in the field, but this has 
not been uniformly successful, and cultural studies have 
shown that the fungus is able to withstand a high percentage 
of alkalinity. Nevertheless, when liming results in the im- 
provement of physical and sanitary conditions of the soil it 
undoubtedly assists in restraining the activity of the fungus 
in an indirect way, possibly by raising the resistance of the 
host. 

Even though the fungus may be widely distributed, it is 
advantageous to plant clean "seed." This applies particu- 
larly to the case of the potato. The presence of the sclerotia 
upon the tuber makes possible the early spread of the fungus 



[Vol. 2 
446 ANNALS OP THE MISSOURI BOTANICAL GARDEN 

to the young shoots. It has been positively determined that 
the more effective tuber treatment is the standard corrosive 
sublimate solution, as for potato scab. In all cases, however, 
it would be better to employ seed which are not infected, if 
this is possible. 

Conclusions and Notes 

In the account already given of Bhisoctonia Grocorum per- 
haps sufficient discussion of the occurrence and the character- 
istics of this form has been entered upon, except in the way 
of a direct comparison between this species and B. Solani, 
subsequently included. Further work upon the first named 
species should consider especially the culture of this organ- 
ism, inoculation experiments, the development of the organ- 
ism as it occurs on several hosts, the formation of sclerotia 
and infection cushions, and the confirmation or more definite 
declination of Eriksson's view that the fungus is referable 
to Corticium {Hypochnus) . From the study of this organism 
thus far the following conclusions seem justified : 

1. The views of L. and C. Tulasne that the forms of Bhi- 
zoctonia on crocus, alfalfa, and other hosts may be included in 
a single morphological species is confirmed. 

2. The correct name of the violet root felt fungus, so long 
as a spore stage remains uncertain, is Bhisoctonia Grocorum 
(Pers.) DC. 

3. This organism occurs throughout a considerable part 
of Europe and has been found in a few localities in America. 

4. It attacks a variety of plants representing many fam- 
ilies, mostly dicotyledonous. 

5. The mycelium and sclerotia exhibit no important dif- 
ferences in equivalent stages on the different hosts, but large 
sclerotia which form freely in contact with crocus, and often 
near the affected roots of alfalfa, are seldom observed in con- 
nection with the attacks upon beets, carrots, and some other 
hosts. 

6. The existence of distinct forms or races of this species 
requires further extended study. 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 447 

7. The organism has not yet proved culturable with the 
usual laboratory methods. 

8. At the present time there is insufficient evidence to de- 
termine what the perfect stage of this organism may be. 

Obviously much still remains to be done regarding the 
physiological, pathological, and taxonomic relationship of the 
culturable forms which in the vegetative stage may be re- 
ferred to the form-genus Rhizoctonia. The writer has grown 
in culture Rhizoctonia from twenty-three different American 
hosts, most of which are mentioned by Duggar and Stewart 
('01). Most of these were grown upon a variety of culture 
media including prune juice, beet, and potato agar ; also beans, 
stems and pods, celery, sugar beet and potato cylinders, and 
corn meal mush. With one exception (the organism from 
rhubarb) the cultural characteristics have been sufficiently 
similar, especially after protracted culture in the laboratory, 
to suggest a single species, with characteristics of the beet 
and cotton fungus, already sufficiently described (Atkinson, 
'92, '95; Duggar, '99). Moreover, these cultural studies have 
confirmed in all cases the conclusions tentatively arrived at 
from the preliminary microscopic examination of the fungus 
on the different hosts. Reasons have already been given to 
indicate why this species is properly R. Solani. It is recog- 
nized, however, that much culture and inoculation work is 
necessary to establish the point that the fungus on the various 
hosts is the same species, and to determine to what extent 
physiological forms may occur. 

The following brief summary of conclusions may be pre- 
sented with regard to Rhizoctonia Solani: 

1. The common American species of Rhizoctonia is R. 
Solani Kiihn. 

2. This fungus is widely distributed in America and else- 
where, and would seem to occur on the potato in most regions 
of the world where this crop is a staple product. 

3. The host plants represent many families of dicot- 
yledons, Asparagus Sprengeri being the only monocotyle- 
donous host thus far reported. 



[Vol. 2 
448 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

4. The types of disease induced are most diverse, damp- 
ing off and root and stem rots being the most important direct 
effects. Secondary effects have been studied only in a few 
localities. 

5. The mycelium and the sclerotia, as well as the general 
appearance on the host, readily distinguish the fungus from 
Rhizoctonia Crocorum (Pers.) DC. 

6. The organism is readily culturable by the usual labora- 
tory methods. 

7. The evidence seems clear that the perfect stage of this 
organism is Corticium vagum B. & C. 

It is to be regretted that the fungus causing a disease of 
rhubarb (Duggar and Stewart, '01) was lost before adequate 
study could be bestowed upon it. The fungus bore a close 
resemblance to. Rhizoctonia, but the aerial hyphal cells were 
shorter and of greater diameter than those of R. Solani. No 
sclerotia were found on the host, and they did riot develop in 
culture. 

Shaw ('13) has contributed interesting notes on diseases 
of plants in India attributed to two species of Rhisoctonia. 
Unfortunately, however, he has added to the general con- 
fusion regarding this subject by a preliminary discussion 
which does not sufficiently designate the forms referred to, 
but more especially by the advancement of certain ideas re- 
garding species which are made, apparently, without adequate 
study of material from other countries. The conclusions ar- 
rived at are necessarily at variance with our present knowl- 
edge of the forms of Rhizoctonia. 

Of the organisms producing diseases in Indian crops he 
refers to Rhizoctonia Solani Kuhn, a fungus which he found 
on jute, mulberry, cotton, groundnut, and cowpea. The mode 
of branching of young hyphae of his fungus is characteristic 
of R. Solani, but with this the resemblance apparently ceases. 
Basing an opinion wholly upon his descriptions and figures, 
the adult mycelium (Shaw, '13, pi. 7 and 8) differs from R. 
Solani (1) in being usually much finer; (2) in the abundant 
development of short "barrel-shaped" cells in the ordinary 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 449 

vegetative mycelium, which would seem, from his figures, to 
have little in common with the chain-like, ovoidal, often 
branched or lobed cells (designated "barrel-shaped" by 
Balls) of R. Solani (see Atkinson, '92, '95; Balls, '05, '06; 
Duggar, '99; Duggar and Stewart, '01; and others) ; and (3) 
in the verrucose or warty, wall markings (Shaw, '13, pi. 8, 
figs. 2-3), all of which indicate some other fungus. 

Again, the development of sclerotia (Shaw, '13, pi. 8, fig. 4) 
discloses a type of hyphal cell not characteristic of R. Solani; 
and the small discrete sclerotia themselves (Shaw, '13, pi. 2, 
fig. 3, pi. 8, fig. 1) convincingly indicate that another fungus 
was under consideration. I can find no record of a description 
of sclerotia resembling these in the literature of Rhizoctonia 
diseases. I am at a loss to understand how a fungus with such 
characteristics could be likened to Kuhn's fungus on the 
potato, even though depending upon Kuhn's imperfect de- 
scription. On the other hand, neither in general appearance 
nor in structure (as described and figured by Shaw) am I 
able to find any resemblance to the "small sclerotia" or in- 
fection cushions of R. Crocorum (R. violacea). 

In moist situations the sclerotia of Rhizoctonia Solani may 
occur on aerial organs (as on the pods of beans, Hedgcock, 
'04, on lettuce leaves, Stone and Smith, '00) but the frequent 
and apparently normal occurrence of minute sclerotia, fairly 
regularly arranged, on the dead tips of stems, as described 
by Shaw, finds no parallel in R. Solani. Again, in regard to 
the hyphae, it may be said that while there is a characteristic 
location of the septum when a branch is formed in a hypha 
of Rhizoctonia, this character alone is not sufficient to identify 
the fungus. It is necessary to take into consideration all of 
the mycelial characteristics which have been referred to, and 
if possible also the cultural characters. The writer finds that 
the "Rhizoctonia type" of branching is more or less similar 
to that found in the hyphae of certain species of Sclerotinia, 
Morchella, Pleospora, Rosellinia, and many others. It would 
be unwise to offer any definite suggestions regarding the 
fungus described by Shaw and referred to above. What rela- 
tion it may bear to the fungus of "bangle blight" (Cunning- 



[Vol. 2 
450 ANNALS OP THE MISSOURI BOTANICAL GARDEN 

ham, '97) must also remain, for the present, uncertain. It is 
possible that Shaw's fungus is one of the Ascomycetes, at 
least this is suggested by the figures of the sclerotia. 

In my opinion Shaw has correctly referred to Gorticium 
vagum B. & C. (accordingly to Rhizoctonia Solani Kuhn, 
representing the vegetative phases of that species) another 
fungus which he also found in India on the groundnut and 
cowpea. Both the mycelium and the sclerotia of this second 
organism as described by him agree with R. Solani as we 
know it on carnation, beet, bean, lettuce, potato, etc., in 
America and elsewhere, as far as reported. The descriptions 
and measurements of basidia and spores are also in sufficient 
accord. 

Shaw has even suggested that Rhizoctonia violacea Tul. is 
the vegetative stage of Gorticium vagum B. & C. No such 
unfortunate confusion could result, however, had he been able 
to study that which is accepted as Kiihn's organism on the 
potato together with the violet root felt fungus of Europe on 
any of its hosts. He has obviously failed to find material of 
the last named fungus in his studies thus far. 

Between Rhizoctonia Grocorum and R. Solani in the vege- 
tative condition some of the important and easily observed 
contrasting features as usually found are presented in the 
following table : 

Rhizoctonia Crocorum Rhizoctonia Solani 

An external felt, or mantle, of External mycelium, if notice- 
investing hyphae, confined able, only a web, or some- 
almost exclusively to under- times with flaky tufts, the 
ground organs. formation of a "collar" oc- 

curring only at the time of 
fruiting. 
Color of mycelial felt pink-red Color of web, if evident, dirty 
or violet to violet-brown yellow to yellow-brown, 
with age. 
Protoplasm of young hyphal Young hyphal cells hyaline, 
cells soon develops a violet and even when flavous later, 
reddish pigment. pigment confined to walls. 

Infection cushions conspicu- Nothing comparable to infec- 
ous in the root-investing tion cushions, though on 
mycelium on most hosts. potato sclerotia may serve 

as points of infection. 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 451 

Sclerotia, when present, Sclerotia normally free from 
densely wooly with invest- any definite or permanent 
ing mycelium and filaments investment of mycelium, or 
of short, ovoidal or ellip- filaments of elbowed hyphal 
tical hyphal cells. Internal cells. Internal structure 
structure not truly plec- homogeneous in the larger, 
tenchymatic, cells variable denser sclerotia. 
in size. 

Cultures difficult, — not yet ob- Cultures readily obtained on 
tained by usual methods. any nutrient medium. 

Typically a parasite, with per- Grows rapidly saprophytic- 
haps the possibility of con- ally on the invaded host, 
tinuing existence only for a and apparently on debris in 
time saprophytically. the soil when conditions are 

favorable. 

The following species may be excluded from Rhisoctonia 
as far as can be judged from reference to the descriptions 
and to the exsiccati material examined: 

Rhisoctonia AIM Graves, de Thuemen, Myc. Univ. Fasc. 
6: 600 (obviously not closely related to the forms here dis- 
cussed). R. bicolor Ell. N. Am. Fung. Fasc. 10: 977 (with 
sclerotia like those of a Botrytis, e. g., B. cinerea) . R. Bras- 
sicarum Lib., Libert, PL Crypt. Arduennae, Fasc. 3 : 240 (no 
characteristics of Rhisoctonia). R. muscorum Fr. Ellis, N. 
Am. Fung. Fasc. 13 -.1266; Libert, PL Crypt. Arduennae, 
Fasc. 2 -.141. 

From the descriptions alone it would seem that the follow- 
ing species have insufficient affinities with Rhisoctonia to be 
included, but critical study of material is needed: 

Rhisoctonia aurantiaca Ell. & Ev. on decaying wood of 
Acer; R. Batatas Fr. on Ipomoea Batatas; R. placenta Schw., 
and R. radiciformis Schw., on decaying wood (the three last 
mentioned are distributed in Schweinitz', Syn. N. Am. Fung., 
to which, however, the writer has not yet had access) ; R. 
destruens Tassi, reported parasitic on five species of Del- 
phinium, and on Lobelia laxiflora, and Hibiscus rosa-sinensis; 
R. moniliformis Ell. & Ev. on branches of Nyssa. 

Rhisoctonia Strobi Scholz ('97) on roots of Finns strobus 
in Austria, is insufficiently described to warrant a suggestion ; 
and R. subepigea Bertoni ( '97) on coffee should be included in 
a further comparative study. 



[Vol. 2 
452 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

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Johnson, J. ('14). The control of damping-off disease in plant beds. Wis. Agr. 
Exp. Sta., Res. Bull. 31 : 29-61. 1914. 

Jones, L. R. ('07). The black leg disease of the potato. Vt. Agr. Exp. Sta., 
Bull. 129: 101-103. 1907. 

Kickx, J. ('67). Flore cryptogamique des Flandres 2: p. 470. 1867. 

Ktthn, J. ('58). Krankheiten der Kulturgewachse, ihre Ursachen und ihre 
Verhtitung. pp. 222-228, 228-239, 243-249. f. 3-22. 185,8^ 

Laubert, ('06). Bot. Centralbl. 102:525-527. 1906. 

L6veilh5, J. H. ('43). Memoire sur le genre Sclerotium. Ann. d. Sci. Nat. Bot. 
20 : 218-248. pi 6-7. 1843. 

Lindau, G. ('09). Rabenhorst's Cryptogamen-Flora v. Deutschland, Oesterreich, 
u. d. Schweisz. 19; 683-686. 1909. 

Link, H. F. (1824). Hyphomycetes. Linnaeus, Spec. Plant., ed. 4, cur. Willdenow. 
61 : pp. 119-120. Berlin, 1824. 

Ltistner, G. ('03). Beobachtungen fiber den Wurzelt&ter der Luzerne (Rhizoctonia, 
violacea Tul.). K. Lehranst. f. Wein-, Obst-, u. Gartenbau zu Geisenheim a 
Rh. 1902 : 200-203. f. 47. 1903. 

Lyon, T. L. and Wianco, A. T. ('02). Diseases of sugar beets. Nebr. Agr. Exp. 
Sta., Bull. 73 : 21-23. 1902. 

McAlpine, D. ('11). Rhizoctonia rot, or potato collar fungus. Handbook of 
fungous diseases of the potato in Australia and their treatment, pp. 60-65. 
pi. 9-18, 19, 39-48. 1911. (cf. pp. 75-77.) 

McCready, S. B. ('10). Pod and stem rot of beans (Rhizoctonia). Ont. Agr. 

Coll. and Exp. Farms, Rept. 36 : 46-47. f. 6. 1910. 
Montague, C. ('50). Etude micrographique de la maladie du safran, connue 

sous le nom de Tacon. Soc. de Biol., Paris, Mem. 1 [1849] : 63-68. 1850. 

[Translation by Berkeley, Jour. Hort. Soc. London 5:21-25. 1850.] 
Morse W. J. and Shapovalow, M. ('14). The Rhizoctonia disease of potato. 

Me. Agr. Exp. Sta., Bull. 230 : 193-216. f. 61-73. 1914. 
Nees von Esenbech, (1816). Das System der Pilze und Schw'amme. p. 148. 

Wurzburg, 1816. 



[Vol. 2 
456 ANNALS OP THE MISSOURI BOTANICAL GARDEN 

Nelson, A. ('07). Some potato diaeasea. Wyo. Agr. Exp. Sta., Bull. 71 : 1-39. 
f. 1-11. 1907. 

Norton, J. B. S. ('06). Irish potato diseases. Md. Agr. Exp. Sta., Bull. 108 : 
63-72. f. 1-4. 1906. 

Orton, W. A. ('14). Potato wilt, leaf-roll, and related diseases. U. S. Dept. 
Agr. Bull. 64: pp. 40-41. pi. 15. 1914. 

Pammel, L. H. ('91). Fungous diseases of the sugar beet. la. Agr. Exp. Sta., 
Bull. 15: 234-254. pi. 1-7. 1891. [See Preliminary notes on a root-rot disease 
of sugar beets, pp. 243-251. pi. 3-6.] 

Peglion, V. ('97). II mal vinato della medica e delle barbietole. Bol. di Entom. 
Agron. e Patol. Veg. 4 : 367-369. Padua, 1897. 

Peltier, G. L. ('14). Rhizoctonia in America. Phytopath. 4:406. 1914. 

Persoon, C. H. (1801). Synopsis methodica fungorum. pp. 119-120. 1801. 

Pethybridge, G. H. ('10). Potato diseases in Ireland. Dept. Agr. and Tech. 
Instr. for Ireland, Jour. 10: 1-18. f. 1-8. 1910. 



-, ('10a). A little known potato disease. Garden 74:560. f. 1. 1910. 
-, ('11). Investigations on potato diseases (second report). Dept. Agr. 



and Tech. Instr. for Ireland, Jour. 11:29-32. f. 11-U. 1911. 

-, ('15). "Black speck" scab and "collar fungus." Ibid. 15:513-517. 



1915. 
Pierson,W. R. ('02). Sterilized soil for stem rot. Gardening 10: 179-181. 1902. 

Potel, H. ('00). Molestias cryptogamicas da batata ingleza e seu tractamento. 
Bol. da Agr. Estado de Sao Paulo 1 : 45-48. 1900. [See p. 46.] 

Prillieux, E. ('83). Etude sur deux maladies du safran. Ann. de l'Inst. Nat. 
Agron. 6: 17-31. pi. 8-4. 1883. 

, ('91). Sur la penetration de la Rhizoctone violette dans les racines 

de la betterave et de la luzerne. Compt. rend. acad. Paris 113: 1072-1074. 
1891. 

, ('96). Ibid. Soc. Bot. de Prance, Bull. 43 : 9-11. f. 1. 1896. 

1 , ('97). Maladies des plantes agricoles 2:144-157. f. 282-287. 1897. 

— , et Delacroix, G. ('91). Hypochnus Solani nov. sp. Soc. Myc. France, 

Bull. 7:220-221. f. 1. 1891. 

Prunet, A. ('93). Sur le Rhizoctone de la lucerne. Compt. rend. acad. Paris 
117:252-255. 1893. 

Riehm, E. ('11 ). Ueber den Zusammenhang zwischen Rhizoctonia Solani Kiihn 
und Hypochnus Solani Prill, u. Del. K. Biol. Anstalt f. Landw.- u. Forstw., 
Mitt. 6: p. 23. Berlin, 1911. 

Rolfs, F. M. ('03). Corticium vagum B. and C. var. Solani Burt. Science, N. S. 
18:729.1903. 

, ('02, '04). Potato failures. Colo. Agr. Exp. Sta., Bull. 70:1-20. 

pi. 1-12. 1902; 91: 1-33. pi. 1-5. 1904. 

-, ('05). (Tomato diseases) Corticium vagum (B. and C). Fla. Agr. 



Exp. Sta., Rept. 1905 : 46-47. 1905. 
Rostrup, E. ('86). Undersgelser angaaende Svampeslaegten Rhizoctonia. K. 
Dans. Vid. Sels. Forhandl. 1886 : 59-77. pi. 1-2. 1886. 



1915] 

DUGGAR RHIZOCTONIA CROCORUM AND R. SOLANI 457 

Roze, E. ('96). Observations sur le rhizocfcone de la pomme de terre. Compt. 
rend. acad. Paris, 123:1017-1019. 1896. 

, ('97). La maladie de la gale de la pomme de terre et ses rapports 

avec le Khizoctonia Solani Kiihn. Soc. Myc. de France, Bull. 13 : 23-28. 1897. 

Saccardo, P. A. ('99). Syll. Fung. 14: pp. 1175-1177. 1899. 

Salmon, E. S. ('08). Disease of seakale. Gardeners' Chronicle 44:1-3. f. 1-3. 
1908. 

-, and Crompton, T. E. ( '08 ) . The Rhizoctonia disease of seakale. S. E. 



Agr. Coll., Wye, Jour. 17 : 348-353. pi. 21-25. 1908. 

Scholz, E. R. ('97). Rhizoctonia Strobi, ein neuer Parasit der Weymouthskiefer. 
K. K. Zool.- Bot. Akad. Ges., Verhandl. 47 : 541-557. f. 1-6. 1897. 

Selby, A. D. ('02). A disease of potato stems in Ohio, due to Rhizoctonia. 
Science, N. S. 16: 138. 1902. 

-, ('03). A rosette disease of potatoes. Ohio Agr. Exp. Sta., Bull. 139 : 



51-66. f. 1-5. 1903. 

-, ('03a, '06). Studies in potato rosette II. Ibid. 145 : 13-28. f. 1-4. 



1903. [cf. also, Circ. 57 : 1-7. 1906; and 59 : 1-3. 1906.] 
, ('04). Tobacco diseases, bed rot. Ibid. 156 : pp. 97-99. pi. 1. 1904. 



Shaw, F. J. F. ('13). The morphology and parasitism of Rhizoctonia. Dept. 
Agr. India, Mem. 6: 115-153. pi. 1-11. 1913. 

Sorauer, P. ('86). Pflanzenkrankheiten. pp. 354-361. 1886. (2d ed.) 

, ('08). Ibid. 2:471-474. 1908. (3d ed., revised~by Lindau 1908.) 

Stevens, F. L. ('13). The fungi which cause plant disease. Rhizoctonia. pp. 
406-408. f. 298-294; pp. 659-660. 1913. 



, and Hall, J. 6. ( '09 ) . Hypochnose of pomaceous fruits. Ann. Myco- 

logici 7:49-59. f. 1-8. 1909. 

, and Wilson, G. W. ('11). N. C. Agr. Exp. Sta., Rept. 1911 : 70-73. 1911. 



Stewart, F. C, French, D. T., and Wilson, J. K. ('08). Troubles of alfalfa in 
New York. N. Y. Agr. Exp. Sta., Bull. 305 : 330-416. pi. 1-11. 1908. [See 
Root-rot and damping off. pp. 392-393.] 

Stift, A. ('00). Der WurzeltSdter Oder die Rotfaule der Ruben (Rhizoctonia 
violacea Tul.). Die Krankheiten der Zuckerrube. pp. 67-72. pi. 8-9. Wien, 
1900. 

-, ('13). Zur Geschichte des WurzeltSdters oder der Rothfaule (Rhiz- 



octonia violacea Tul.). Oesterr.-Ungar. Zeitschr. f. Zuckerind. u. Landw. 
42 : 445-461. 1913. 

Stoklasa, J. ('98). Wurzelbrand der Zuckerrube. Centralbl. f. Bakt. II. 4: 
687-694. 1898. 

Stone, G. E. and Smith, R. E. ( '00 ) . The rotting of greenhouse lettuce. Mass. 
Agr. Exp. Sta., Bull. 69 : 1-40. /. 1-10. 1900. [See A Rhizoctonia disease of 
lettuce, pp. 16-17. f. 8-10.] 

, , ('02). Carnation stem rot. Mass. Agr. Exp. Sta., Rept. 

14:67-68. 1902. 

Tassi, F. ('00). Di una nuova Rhizoctonia. Bui. de Lab. ed Orto Bot. Siena 
3 : 49-51. pi. 4, f. A-M. 1900. 



[Vol. 2, 1916] 
458 ANNALS OF THE MISSOURI BOTANICAL GARDEN 

Taubenhaus, J. J. ('14). The diseases of the sweet pea. Del. Agr. Exp. Sta., 
Bull. 106: 1-93. f. 1-4$. 1914. [See Root rot. pp. 18-27. f. 9-11.] 

Tubeuf, K. von ('97). [Trans, by W. G. Smith.] Diseases of plants induced 
by cryptogamic parasites, pp. 201-202. 1897. 

Tulasne, L. et C. ('62). Fungi Hypogaei. pp. 188-195. pi. 8, f. 4; pi. 9; pl.20, 
f. 3-4. 1862. 

Van Hook, J. M. ('04). Diseases of ginseng. Cornell Univ. Agr. Exp. Sta., Bull. 
219 : 277-303. /. 18-42. 1904. [See Damping off by Rhizoctoma. pp. 289- 
291. /. 82-83.] 

Webber, H. J. ('90). Catalogue of the flora of Nebraska. Nebr. State Bd. 
Geol., Rept. 1889 : p. 216. 1890. 

Whetzel, H. H. and Rosenbaum, J. ('12). The diseases of ginseng and their 
control. U. S. Dept. Agr., Bur. PI. Ind., Bull. 250 : 1-44. pi. 1-12. 1912. 
[See Damping-off of seedlings, pp. 22-23.] 

Westendorp, G. D. ('52). Notice sur quelques Cryptogames inedites ou nouvelles 
pour la flore beige. Acad. Roy. Belg., Bull. 18 a : p. 402. 1852. 

Winter, G. Die Pilze. [In Rabenhorst's Cryptogamen-Flora von Deutschland, 
Oesterreich, u. d. Schweiz l a : p. 277.] 

Wolf, P. A. ('14). Fruit rots of egg plant. Phytopath. 4:38. 1914. 

Wollenweber, H. W. ('13). Pilzparasitare Welkekrankheiten der Kulturpflanze. 
Ber. d. deut. bot. Ges. 31 : 17-33. 1913. [See Rhizoctonia. p. 30.]